scheme.c

/* T I N Y S C H E M E    1 . 4 2
 *   Dimitrios Souflis (dsouflis@acm.org)
 *   Based on MiniScheme (original credits follow)
 * (MINISCM)               coded by Atsushi Moriwaki (11/5/1989)
 * (MINISCM)           E-MAIL :  moriwaki@kurims.kurims.kyoto-u.ac.jp
 * (MINISCM) This version has been modified by R.C. Secrist.
 * (MINISCM)
 * (MINISCM) Mini-Scheme is now maintained by Akira KIDA.
 * (MINISCM)
 * (MINISCM) This is a revised and modified version by Akira KIDA.
 * (MINISCM)    current version is 0.85k4 (15 May 1994)
 *
 */

#include "scheme-private.h"
#ifdef WIN32
#define snprintf _snprintf
#endif
#if USE_MATH
#include <math.h>
#endif

#include <ctype.h>

#define TOK_EOF (-1)
#define TOK_LPAREN 0
#define TOK_RPAREN 1
#define TOK_DOT 2
#define TOK_ATOM 3
#define TOK_QUOTE 4
#define TOK_COMMENT 5
#define TOK_DQUOTE 6
#define TOK_BQUOTE 7
#define TOK_COMMA 8
#define TOK_ATMARK 9
#define TOK_SHARP 10
#define TOK_SHARP_CONST 11
#define TOK_VEC 12

#define BACKQUOTE '`'
#define DELIMITERS "()\";\f\t\v\n\r "

/*
 *  Basic memory allocation units
 */

#define banner "TinyScheme 1.42"

#include <string.h>
#include <stdlib.h>

#ifndef prompt
#define prompt "ts> "
#endif

#ifndef InitFile
#define InitFile "init.scm"
#endif

#ifndef FIRST_CELLSEGS
#define FIRST_CELLSEGS 3
#endif

enum scheme_types {
	T_STRING = 1,
	T_NUMBER = 2,
	T_SYMBOL = 3,
	T_PROC = 4,
	T_PAIR = 5,
	T_CLOSURE = 6,
	T_CONTINUATION = 7,
	T_FOREIGN = 8,
	T_CHARACTER = 9,
	T_PORT = 10,
	T_VECTOR = 11,
	T_MACRO = 12,
	T_PROMISE = 13,
	T_ENVIRONMENT = 14,
	T_LAST_SYSTEM_TYPE = 14
};

/* ADJ is enough slack to align cells in a TYPE_BITS-bit boundary */
#define ADJ 32
#define TYPE_BITS 5
#define T_MASKTYPE 31 /* 0000000000011111 */
#define T_SYNTAX 4096 /* 0001000000000000 */
#define T_IMMUTABLE 8192 /* 0010000000000000 */
#define T_ATOM 16384 /* 0100000000000000 */ /* only for gc */
#define CLRATOM 49151 /* 1011111111111111 */ /* only for gc */
#define MARK 32768 /* 1000000000000000 */
#define UNMARK 32767 /* 0111111111111111 */

static num num_add(num a, num b);
static num num_mul(num a, num b);
static num num_div(num a, num b);
static num num_intdiv(num a, num b);
static num num_sub(num a, num b);
static num num_rem(num a, num b);
static num num_mod(num a, num b);
static int num_eq(num a, num b);
static int num_gt(num a, num b);
static int num_ge(num a, num b);
static int num_lt(num a, num b);
static int num_le(num a, num b);

#if USE_MATH
static double round_per_R5RS(double x);
#endif
static int is_zero_double(double x);
static int num_is_integer(pointer p)
{
	return ((p)->_object._number.is_fixnum);
}

static num num_zero;
static num num_one;

int is_string(pointer p)
{
	return (type(p) == T_STRING);
}
static int is_list(scheme *sc, pointer p);
int is_vector(pointer p)
{
	return (type(p) == T_VECTOR);
}
static void fill_vector(pointer vec, pointer obj);
static pointer vector_elem(pointer vec, int ielem);
static pointer set_vector_elem(pointer vec, int ielem, pointer a);
int is_number(pointer p)
{
	return (type(p) == T_NUMBER);
}
int is_integer(pointer p)
{
	if (!is_number(p))
		return 0;
	if (num_is_integer(p) || (double)ivalue(p) == rvalue(p))
		return 1;
	return 0;
}

int is_real(pointer p)
{
	return is_number(p) && (!(p)->_object._number.is_fixnum);
}

int is_character(pointer p)
{
	return (type(p) == T_CHARACTER);
}
char *string_value(pointer p)
{
	return strvalue(p);
}
num nvalue(pointer p)
{
	return ((p)->_object._number);
}
long ivalue(pointer p)
{
	return (num_is_integer(p) ? (p)->_object._number.value.ivalue :
					  (long)(p)->_object._number.value.rvalue);
}
double rvalue(pointer p)
{
	return (!num_is_integer(p) ? (p)->_object._number.value.rvalue :
					   (double)(p)->_object._number.value.ivalue);
}
long charvalue(pointer p)
{
	return ivalue_unchecked(p);
}
int is_port(pointer p)
{
	return (type(p) == T_PORT);
}
int is_inport(pointer p)
{
	return is_port(p) && p->_object._port->kind & port_input;
}
int is_outport(pointer p)
{
	return is_port(p) && p->_object._port->kind & port_output;
}
int is_pair(pointer p)
{
	return (type(p) == T_PAIR);
}
pointer pair_car(pointer p)
{
	return car(p);
}
pointer pair_cdr(pointer p)
{
	return cdr(p);
}
pointer set_car(pointer p, pointer q)
{
	return car(p) = q;
}
pointer set_cdr(pointer p, pointer q)
{
	return cdr(p) = q;
}
int is_symbol(pointer p)
{
	return (type(p) == T_SYMBOL);
}
char *symname(pointer p)
{
	return strvalue(car(p));
}
int is_syntax(pointer p)
{
	return (typeflag(p) & T_SYNTAX);
}
int is_proc(pointer p)
{
	return (type(p) == T_PROC);
}
int is_foreign(pointer p)
{
	return (type(p) == T_FOREIGN);
}
char *syntaxname(pointer p)
{
	return strvalue(car(p));
}
static const char *procname(pointer x);
int is_closure(pointer p)
{
	return (type(p) == T_CLOSURE);
}
int is_macro(pointer p)
{
	return (type(p) == T_MACRO);
}
pointer closure_code(pointer p)
{
	return car(p);
}
pointer closure_env(pointer p)
{
	return cdr(p);
}
int is_continuation(pointer p)
{
	return (type(p) == T_CONTINUATION);
}
/* To do: promise should be forced ONCE only */
int is_promise(pointer p)
{
	return (type(p) == T_PROMISE);
}
int is_environment(pointer p)
{
	return (type(p) == T_ENVIRONMENT);
}
int is_immutable(pointer p)
{
	return (typeflag(p) & T_IMMUTABLE);
}
void setimmutable(pointer p)
{
	typeflag(p) |= T_IMMUTABLE;
}

static int Cisalpha(int c)
{
	return isascii(c) && isalpha(c);
}
static int Cisdigit(int c)
{
	return isascii(c) && isdigit(c);
}
static int Cisspace(int c)
{
	return isascii(c) && isspace(c);
}
static int Cisupper(int c)
{
	return isascii(c) && isupper(c);
}
static int Cislower(int c)
{
	return isascii(c) && islower(c);
}

static const char *charnames[32] = { "nul", "soh", "stx", "etx", "eot", "enq",
				     "ack", "bel", "bs",  "ht",	 "lf",	"vt",
				     "ff",  "cr",  "so",  "si",	 "dle", "dc1",
				     "dc2", "dc3", "dc4", "nak", "syn", "etb",
				     "can", "em",  "sub", "esc", "fs",	"gs",
				     "rs",  "us" };

static int is_ascii_name(const char *name, int *pc)
{
	int i;
	for (i = 0; i < 32; i++) {
		if (strcmp(name, charnames[i]) == 0) {
			*pc = i;
			return 1;
		}
	}
	if (strcmp(name, "del") == 0) {
		*pc = 127;
		return 1;
	}
	return 0;
}

static int file_push(scheme *sc, const char *fname);
static void file_pop(scheme *sc);
static int is_one_of(char *s, int c);
static int alloc_cellseg(scheme *sc, int n);
static long binary_decode(const char *s);
static pointer get_cell(scheme *sc, pointer a, pointer b);
static pointer _get_cell(scheme *sc, pointer a, pointer b);
static pointer reserve_cells(scheme *sc, int n);
static pointer get_consecutive_cells(scheme *sc, int n);
static pointer find_consecutive_cells(scheme *sc, int n);
static void finalize_cell(scheme *sc, pointer a);
static int count_consecutive_cells(pointer x, int needed);
static pointer find_slot_in_env(scheme *sc, pointer env, pointer sym, int all);
static pointer mk_number(scheme *sc, num n);
static char *store_string(scheme *sc, int len, const char *str, char fill);
static pointer mk_vector(scheme *sc, int len);
static pointer mk_atom(scheme *sc, char *q);
static pointer mk_sharp_const(scheme *sc, char *name);
static pointer mk_port(scheme *sc, port *p);
static pointer port_from_filename(scheme *sc, const char *fn, int prop);
static pointer port_from_file(scheme *sc, FILE *, int prop);
static pointer port_from_string(scheme *sc, char *start, char *past_the_end,
				int prop);
static port *port_rep_from_filename(scheme *sc, const char *fn, int prop);
static port *port_rep_from_file(scheme *sc, FILE *, int prop);
static port *port_rep_from_string(scheme *sc, char *start, char *past_the_end,
				  int prop);
static void port_close(scheme *sc, pointer p, int flag);
static void mark(pointer a);
static void gc(scheme *sc, pointer a, pointer b);
static int basic_inchar(port *pt);
static int inchar(scheme *sc);
static void backchar(scheme *sc, int c);
static char *readstr_upto(scheme *sc, char *delim);
static pointer readstrexp(scheme *sc);
static int skipspace(scheme *sc);
static int token(scheme *sc);
static void printslashstring(scheme *sc, char *s, int len);
static void atom2str(scheme *sc, pointer l, int f, char **pp, int *plen);
static void printatom(scheme *sc, pointer l, int f);
static pointer mk_proc(scheme *sc, enum scheme_opcodes op);
static pointer mk_closure(scheme *sc, pointer c, pointer e);
static pointer mk_continuation(scheme *sc, pointer d);
static pointer reverse(scheme *sc, pointer a);
static pointer reverse_in_place(scheme *sc, pointer term, pointer list);
static pointer revappend(scheme *sc, pointer a, pointer b);
static void dump_stack_mark(scheme *);
static pointer opexe_0(scheme *sc, enum scheme_opcodes op);
static pointer opexe_1(scheme *sc, enum scheme_opcodes op);
static pointer opexe_2(scheme *sc, enum scheme_opcodes op);
static pointer opexe_3(scheme *sc, enum scheme_opcodes op);
static pointer opexe_4(scheme *sc, enum scheme_opcodes op);
static pointer opexe_5(scheme *sc, enum scheme_opcodes op);
static pointer opexe_6(scheme *sc, enum scheme_opcodes op);
static void Eval_Cycle(scheme *sc, enum scheme_opcodes op);
static void assign_syntax(scheme *sc, char *name);
static int syntaxnum(pointer p);
static void assign_proc(scheme *sc, enum scheme_opcodes, char *name);

#define num_ivalue(n) (n.is_fixnum ? (n).value.ivalue : (long)(n).value.rvalue)
#define num_rvalue(n)                                                          \
	(!n.is_fixnum ? (n).value.rvalue : (double)(n).value.ivalue)

static num num_add(num a, num b)
{
	num ret;
	ret.is_fixnum = a.is_fixnum && b.is_fixnum;
	if (ret.is_fixnum) {
		ret.value.ivalue = a.value.ivalue + b.value.ivalue;
	} else {
		ret.value.rvalue = num_rvalue(a) + num_rvalue(b);
	}
	return ret;
}

static num num_mul(num a, num b)
{
	num ret;
	ret.is_fixnum = a.is_fixnum && b.is_fixnum;
	if (ret.is_fixnum) {
		ret.value.ivalue = a.value.ivalue * b.value.ivalue;
	} else {
		ret.value.rvalue = num_rvalue(a) * num_rvalue(b);
	}
	return ret;
}

static num num_div(num a, num b)
{
	num ret;
	ret.is_fixnum = a.is_fixnum && b.is_fixnum &&
			a.value.ivalue % b.value.ivalue == 0;
	if (ret.is_fixnum) {
		ret.value.ivalue = a.value.ivalue / b.value.ivalue;
	} else {
		ret.value.rvalue = num_rvalue(a) / num_rvalue(b);
	}
	return ret;
}

static num num_intdiv(num a, num b)
{
	num ret;
	ret.is_fixnum = a.is_fixnum && b.is_fixnum;
	if (ret.is_fixnum) {
		ret.value.ivalue = a.value.ivalue / b.value.ivalue;
	} else {
		ret.value.rvalue = num_rvalue(a) / num_rvalue(b);
	}
	return ret;
}

static num num_sub(num a, num b)
{
	num ret;
	ret.is_fixnum = a.is_fixnum && b.is_fixnum;
	if (ret.is_fixnum) {
		ret.value.ivalue = a.value.ivalue - b.value.ivalue;
	} else {
		ret.value.rvalue = num_rvalue(a) - num_rvalue(b);
	}
	return ret;
}

static num num_rem(num a, num b)
{
	num ret;
	long e1, e2, res;
	ret.is_fixnum = a.is_fixnum && b.is_fixnum;
	e1 = num_ivalue(a);
	e2 = num_ivalue(b);
	res = e1 % e2;
	/* remainder should have same sign as second operand */
	if (res > 0) {
		if (e1 < 0) {
			res -= labs(e2);
		}
	} else if (res < 0) {
		if (e1 > 0) {
			res += labs(e2);
		}
	}
	ret.value.ivalue = res;
	return ret;
}

static num num_mod(num a, num b)
{
	num ret;
	long e1, e2, res;
	ret.is_fixnum = a.is_fixnum && b.is_fixnum;
	e1 = num_ivalue(a);
	e2 = num_ivalue(b);
	res = e1 % e2;
	/* modulo should have same sign as second operand */
	if (res * e2 < 0) {
		res += e2;
	}
	ret.value.ivalue = res;
	return ret;
}

static int num_eq(num a, num b)
{
	int ret;
	int is_fixnum = a.is_fixnum && b.is_fixnum;
	if (is_fixnum) {
		ret = a.value.ivalue == b.value.ivalue;
	} else {
		ret = num_rvalue(a) == num_rvalue(b);
	}
	return ret;
}

static int num_gt(num a, num b)
{
	int ret;
	int is_fixnum = a.is_fixnum && b.is_fixnum;
	if (is_fixnum) {
		ret = a.value.ivalue > b.value.ivalue;
	} else {
		ret = num_rvalue(a) > num_rvalue(b);
	}
	return ret;
}

static int num_ge(num a, num b)
{
	return !num_lt(a, b);
}

static int num_lt(num a, num b)
{
	int ret;
	int is_fixnum = a.is_fixnum && b.is_fixnum;
	if (is_fixnum) {
		ret = a.value.ivalue < b.value.ivalue;
	} else {
		ret = num_rvalue(a) < num_rvalue(b);
	}
	return ret;
}

static int num_le(num a, num b)
{
	return !num_gt(a, b);
}

#if USE_MATH
/* Round to nearest. Round to even if midway */
static double round_per_R5RS(double x)
{
	double fl = floor(x);
	double ce = ceil(x);
	double dfl = x - fl;
	double dce = ce - x;
	if (dfl > dce) {
		return ce;
	} else if (dfl < dce) {
		return fl;
	} else {
		if (fmod(fl, 2.0) == 0.0) { /* I imagine this holds */
			return fl;
		} else {
			return ce;
		}
	}
}
#endif

static int is_zero_double(double x)
{
	return x == 0;
}

static long binary_decode(const char *s)
{
	long x = 0;

	while (*s != 0 && (*s == '1' || *s == '0')) {
		x <<= 1;
		x += *s - '0';
		s++;
	}

	return x;
}

/* allocate new cell segment */
static int alloc_cellseg(scheme *sc, int n)
{
	pointer newp;
	pointer last;
	pointer p;
	char *cp;
	long i;
	int k;
	int adj = ADJ;

	if (adj < sizeof(struct cell)) {
		adj = sizeof(struct cell);
	}

	for (k = 0; k < n; k++) {
		if (sc->last_cell_seg >= CELL_NSEGMENT - 1)
			return k;
		cp = (char *)sc->malloc(CELL_SEGSIZE * sizeof(struct cell) +
					adj);
		if (cp == 0)
			return k;
		i = ++sc->last_cell_seg;
		sc->alloc_seg[i] = cp;
		/* adjust in TYPE_BITS-bit boundary */
		if (((unsigned long)cp) % adj != 0) {
			cp = (char *)(adj * ((unsigned long)cp / adj + 1));
		}
		/* insert new segment in address order */
		newp = (pointer)cp;
		sc->cell_seg[i] = newp;
		while (i > 0 && sc->cell_seg[i - 1] > sc->cell_seg[i]) {
			p = sc->cell_seg[i];
			sc->cell_seg[i] = sc->cell_seg[i - 1];
			sc->cell_seg[--i] = p;
		}
		sc->fcells += CELL_SEGSIZE;
		last = newp + CELL_SEGSIZE - 1;
		for (p = newp; p <= last; p++) {
			typeflag(p) = 0;
			cdr(p) = p + 1;
			car(p) = sc->NIL;
		}
		/* insert new cells in address order on free list */
		if (sc->free_cell == sc->NIL || p < sc->free_cell) {
			cdr(last) = sc->free_cell;
			sc->free_cell = newp;
		} else {
			p = sc->free_cell;
			while (cdr(p) != sc->NIL && newp > cdr(p))
				p = cdr(p);
			cdr(last) = cdr(p);
			cdr(p) = newp;
		}
	}
	return n;
}

static pointer get_cell_x(scheme *sc, pointer a, pointer b)
{
	if (sc->free_cell != sc->NIL) {
		pointer x = sc->free_cell;
		sc->free_cell = cdr(x);
		--sc->fcells;
		return (x);
	}
	return _get_cell(sc, a, b);
}

/* get new cell.  parameter a, b is marked by gc. */
static pointer _get_cell(scheme *sc, pointer a, pointer b)
{
	pointer x;

	if (sc->no_memory) {
		return sc->sink;
	}

	if (sc->free_cell == sc->NIL) {
		const int min_to_be_recovered = sc->last_cell_seg * 8;
		gc(sc, a, b);
		if (sc->fcells < min_to_be_recovered ||
		    sc->free_cell == sc->NIL) {
			/* if only a few recovered, get more to avoid fruitless gc's */
			if (!alloc_cellseg(sc, 1) && sc->free_cell == sc->NIL) {
				sc->no_memory = 1;
				return sc->sink;
			}
		}
	}
	x = sc->free_cell;
	sc->free_cell = cdr(x);
	--sc->fcells;
	return (x);
}

/* make sure that there is a given number of cells free */
static pointer reserve_cells(scheme *sc, int n)
{
	if (sc->no_memory) {
		return sc->NIL;
	}

	/* Are there enough cells available? */
	if (sc->fcells < n) {
		/* If not, try gc'ing some */
		gc(sc, sc->NIL, sc->NIL);
		if (sc->fcells < n) {
			/* If there still aren't, try getting more heap */
			if (!alloc_cellseg(sc, 1)) {
				sc->no_memory = 1;
				return sc->NIL;
			}
		}
		if (sc->fcells < n) {
			/* If all fail, report failure */
			sc->no_memory = 1;
			return sc->NIL;
		}
	}
	return (sc->T);
}

static pointer get_consecutive_cells(scheme *sc, int n)
{
	pointer x;

	if (sc->no_memory) {
		return sc->sink;
	}

	/* Are there any cells available? */
	x = find_consecutive_cells(sc, n);
	if (x != sc->NIL) {
		return x;
	}

	/* If not, try gc'ing some */
	gc(sc, sc->NIL, sc->NIL);
	x = find_consecutive_cells(sc, n);
	if (x != sc->NIL) {
		return x;
	}

	/* If there still aren't, try getting more heap */
	if (!alloc_cellseg(sc, 1)) {
		sc->no_memory = 1;
		return sc->sink;
	}

	x = find_consecutive_cells(sc, n);
	if (x != sc->NIL) {
		return x;
	}

	/* If all fail, report failure */
	sc->no_memory = 1;
	return sc->sink;
}

static int count_consecutive_cells(pointer x, int needed)
{
	int n = 1;
	while (cdr(x) == x + 1) {
		x = cdr(x);
		n++;
		if (n > needed)
			return n;
	}
	return n;
}

static pointer find_consecutive_cells(scheme *sc, int n)
{
	pointer *pp;
	int cnt;

	pp = &sc->free_cell;
	while (*pp != sc->NIL) {
		cnt = count_consecutive_cells(*pp, n);
		if (cnt >= n) {
			pointer x = *pp;
			*pp = cdr(*pp + n - 1);
			sc->fcells -= n;
			return x;
		}
		pp = &cdr(*pp + cnt - 1);
	}
	return sc->NIL;
}

/* To retain recent allocs before interpreter knows about them -
   Tehom */

static void push_recent_alloc(scheme *sc, pointer recent, pointer extra)
{
	pointer holder = get_cell_x(sc, recent, extra);
	typeflag(holder) = T_PAIR | T_IMMUTABLE;
	car(holder) = recent;
	cdr(holder) = car(sc->sink);
	car(sc->sink) = holder;
}

static pointer get_cell(scheme *sc, pointer a, pointer b)
{
	pointer cell = get_cell_x(sc, a, b);
	/* For right now, include "a" and "b" in "cell" so that gc doesn't
        think they are garbage. */
	/* Tentatively record it as a pair so gc understands it. */
	typeflag(cell) = T_PAIR;
	car(cell) = a;
	cdr(cell) = b;
	push_recent_alloc(sc, cell, sc->NIL);
	return cell;
}

static pointer get_vector_object(scheme *sc, int len, pointer init)
{
	pointer cells = get_consecutive_cells(sc, len / 2 + len % 2 + 1);
	if (sc->no_memory) {
		return sc->sink;
	}
	/* Record it as a vector so that gc understands it. */
	typeflag(cells) = (T_VECTOR | T_ATOM);
	ivalue_unchecked(cells) = len;
	set_num_integer(cells);
	fill_vector(cells, init);
	push_recent_alloc(sc, cells, sc->NIL);
	return cells;
}

static void ok_to_freely_gc(scheme *sc)
{
	car(sc->sink) = sc->NIL;
}

#if defined TSGRIND
static void check_cell_alloced(pointer p, int expect_alloced)
{
	/* Can't use putstr(sc,str) because callers have no access to
        sc.  */
	if (typeflag(p) & !expect_alloced) {
		fprintf(stderr, "Cell is already allocated!\n");
	}
	if (!(typeflag(p)) & expect_alloced) {
		fprintf(stderr, "Cell is not allocated!\n");
	}
}
static void check_range_alloced(pointer p, int n, int expect_alloced)
{
	int i;
	for (i = 0; i < n; i++) {
		(void)check_cell_alloced(p + i, expect_alloced);
	}
}

#endif

/* Medium level cell allocation */

/* get new cons cell */
pointer _cons(scheme *sc, pointer a, pointer b, int immutable)
{
	pointer x = get_cell(sc, a, b);

	typeflag(x) = T_PAIR;
	if (immutable) {
		setimmutable(x);
	}
	car(x) = a;
	cdr(x) = b;
	return (x);
}

/* ========== oblist implementation  ========== */

#ifndef USE_OBJECT_LIST

static int hash_fn(const char *key, int table_size);

static pointer oblist_initial_value(scheme *sc)
{
	return mk_vector(sc, 461); /* probably should be bigger */
}

/* returns the new symbol */
static pointer oblist_add_by_name(scheme *sc, const char *name)
{
	pointer x;
	int location;

	x = immutable_cons(sc, mk_string(sc, name), sc->NIL);
	typeflag(x) = T_SYMBOL;
	setimmutable(car(x));

	location = hash_fn(name, ivalue_unchecked(sc->oblist));
	set_vector_elem(sc->oblist, location,
			immutable_cons(sc, x,
				       vector_elem(sc->oblist, location)));
	return x;
}

static pointer oblist_find_by_name(scheme *sc, const char *name)
{
	int location;
	pointer x;
	char *s;

	location = hash_fn(name, ivalue_unchecked(sc->oblist));
	for (x = vector_elem(sc->oblist, location); x != sc->NIL; x = cdr(x)) {
		s = symname(car(x));
		/* case-insensitive, per R5RS section 2. */
		if (strcmp(name, s) == 0) {
			return car(x);
		}
	}
	return sc->NIL;
}

static pointer oblist_all_symbols(scheme *sc)
{
	int i;
	pointer x;
	pointer ob_list = sc->NIL;

	for (i = 0; i < ivalue_unchecked(sc->oblist); i++) {
		for (x = vector_elem(sc->oblist, i); x != sc->NIL; x = cdr(x)) {
			ob_list = cons(sc, x, ob_list);
		}
	}
	return ob_list;
}

#else

static pointer oblist_initial_value(scheme *sc)
{
	return sc->NIL;
}

static pointer oblist_find_by_name(scheme *sc, const char *name)
{
	pointer x;
	char *s;

	for (x = sc->oblist; x != sc->NIL; x = cdr(x)) {
		s = symname(car(x));
		/* case-insensitive, per R5RS section 2. */
		if (strcmp(name, s) == 0) {
			return car(x);
		}
	}
	return sc->NIL;
}

/* returns the new symbol */
static pointer oblist_add_by_name(scheme *sc, const char *name)
{
	pointer x;

	x = immutable_cons(sc, mk_string(sc, name), sc->NIL);
	typeflag(x) = T_SYMBOL;
	setimmutable(car(x));
	sc->oblist = immutable_cons(sc, x, sc->oblist);
	return x;
}
static pointer oblist_all_symbols(scheme *sc)
{
	return sc->oblist;
}

#endif

static pointer mk_port(scheme *sc, port *p)
{
	pointer x = get_cell(sc, sc->NIL, sc->NIL);

	typeflag(x) = T_PORT | T_ATOM;
	x->_object._port = p;
	return (x);
}

pointer mk_foreign_func(scheme *sc, foreign_func f)
{
	pointer x = get_cell(sc, sc->NIL, sc->NIL);

	typeflag(x) = (T_FOREIGN | T_ATOM);
	x->_object._ff = f;
	return (x);
}

pointer mk_character(scheme *sc, int c)
{
	pointer x = get_cell(sc, sc->NIL, sc->NIL);

	typeflag(x) = (T_CHARACTER | T_ATOM);
	ivalue_unchecked(x) = c;
	set_num_integer(x);
	return (x);
}

/* get number atom (integer) */
pointer mk_integer(scheme *sc, long num)
{
	pointer x = get_cell(sc, sc->NIL, sc->NIL);

	typeflag(x) = (T_NUMBER | T_ATOM);
	ivalue_unchecked(x) = num;
	set_num_integer(x);
	return (x);
}

pointer mk_real(scheme *sc, double n)
{
	pointer x = get_cell(sc, sc->NIL, sc->NIL);

	typeflag(x) = (T_NUMBER | T_ATOM);
	rvalue_unchecked(x) = n;
	set_num_real(x);
	return (x);
}

static pointer mk_number(scheme *sc, num n)
{
	if (n.is_fixnum) {
		return mk_integer(sc, n.value.ivalue);
	} else {
		return mk_real(sc, n.value.rvalue);
	}
}

/* allocate name to string area */
static char *store_string(scheme *sc, int len_str, const char *str, char fill)
{
	char *q;

	q = (char *)sc->malloc(len_str + 1);
	if (q == 0) {
		sc->no_memory = 1;
		return sc->strbuff;
	}
	if (str != 0) {
		snprintf(q, len_str + 1, "%s", str);
	} else {
		memset(q, fill, len_str);
		q[len_str] = 0;
	}
	return (q);
}

/* get new string */
pointer mk_string(scheme *sc, const char *str)
{
	return mk_counted_string(sc, str, strlen(str));
}

pointer mk_counted_string(scheme *sc, const char *str, int len)
{
	pointer x = get_cell(sc, sc->NIL, sc->NIL);
	typeflag(x) = (T_STRING | T_ATOM);
	strvalue(x) = store_string(sc, len, str, 0);
	strlength(x) = len;
	return (x);
}

pointer mk_empty_string(scheme *sc, int len, char fill)
{
	pointer x = get_cell(sc, sc->NIL, sc->NIL);
	typeflag(x) = (T_STRING | T_ATOM);
	strvalue(x) = store_string(sc, len, 0, fill);
	strlength(x) = len;
	return (x);
}

static pointer mk_vector(scheme *sc, int len)
{
	return get_vector_object(sc, len, sc->NIL);
}

static void fill_vector(pointer vec, pointer obj)
{
	int i;
	int num = ivalue(vec) / 2 + ivalue(vec) % 2;
	for (i = 0; i < num; i++) {
		typeflag(vec + 1 + i) = T_PAIR;
		setimmutable(vec + 1 + i);
		car(vec + 1 + i) = obj;
		cdr(vec + 1 + i) = obj;
	}
}

static pointer vector_elem(pointer vec, int ielem)
{
	int n = ielem / 2;
	if (ielem % 2 == 0) {
		return car(vec + 1 + n);
	} else {
		return cdr(vec + 1 + n);
	}
}

static pointer set_vector_elem(pointer vec, int ielem, pointer a)
{
	int n = ielem / 2;
	if (ielem % 2 == 0) {
		return car(vec + 1 + n) = a;
	} else {
		return cdr(vec + 1 + n) = a;
	}
}

/* get new symbol */
pointer mk_symbol(scheme *sc, const char *name)
{
	pointer x;

	/* first check oblist */
	x = oblist_find_by_name(sc, name);
	if (x != sc->NIL) {
		return (x);
	} else {
		x = oblist_add_by_name(sc, name);
		return (x);
	}
}

pointer gensym(scheme *sc)
{
	pointer x;
	char name[40];

	for (;; sc->gensym_cnt++) {
		snprintf(name, 40, "gensym-%ld", sc->gensym_cnt);

		/* first check oblist */
		x = oblist_find_by_name(sc, name);

		if (x != sc->NIL) {
			continue;
		} else {
			x = oblist_add_by_name(sc, name);
			return (x);
		}
	}

	return sc->NIL;
}

/* make symbol or number atom from string */
static pointer mk_atom(scheme *sc, char *q)
{
	char c, *p;
	int has_dec_point = 0;
	int has_fp_exp = 0;

#if USE_COLON_HOOK
	if ((p = strstr(q, "::")) != 0) {
		*p = 0;
		return cons(sc, sc->COLON_HOOK,
			    cons(sc,
				 cons(sc, sc->QUOTE,
				      cons(sc, mk_atom(sc, p + 2), sc->NIL)),
				 cons(sc, mk_symbol(sc, q), sc->NIL)));
	}
#endif

	p = q;
	c = *p++;
	if ((c == '+') || (c == '-')) {
		c = *p++;
		if (c == '.') {
			has_dec_point = 1;
			c = *p++;
		}
		if (!isdigit(c)) {
			return (mk_symbol(sc, q));
		}
	} else if (c == '.') {
		has_dec_point = 1;
		c = *p++;
		if (!isdigit(c)) {
			return (mk_symbol(sc, q));
		}
	} else if (!isdigit(c)) {
		return (mk_symbol(sc, q));
	}

	for (; (c = *p) != 0; ++p) {
		if (!isdigit(c)) {
			if (c == '.') {
				if (!has_dec_point) {
					has_dec_point = 1;
					continue;
				}
			} else if ((c == 'e') || (c == 'E')) {
				if (!has_fp_exp) {
					has_dec_point =
						1; /* decimal point illegal
                                               from now on */
					p++;
					if ((*p == '-') || (*p == '+') ||
					    isdigit((int)*p)) {
						continue;
					}
				}
			}
			return (mk_symbol(sc, q));
		}
	}
	if (has_dec_point) {
		return mk_real(sc, atof(q));
	}
	return (mk_integer(sc, atol(q)));
}

/* make constant */
static pointer mk_sharp_const(scheme *sc, char *name)
{
	long x;
	char tmp[STRBUFFSIZE];

	if (!strcmp(name, "t"))
		return (sc->T);
	else if (!strcmp(name, "f"))
		return (sc->F);
	else if (*name == 'o') { /* #o (octal) */
		snprintf(tmp, STRBUFFSIZE, "0%s", name + 1);
		sscanf(tmp, "%lo", (long unsigned *)&x);
		return (mk_integer(sc, x));
	} else if (*name == 'd') { /* #d (decimal) */
		sscanf(name + 1, "%ld", (long int *)&x);
		return (mk_integer(sc, x));
	} else if (*name == 'x') { /* #x (hex) */
		snprintf(tmp, STRBUFFSIZE, "0x%s", name + 1);
		sscanf(tmp, "%lx", (long unsigned *)&x);
		return (mk_integer(sc, x));
	} else if (*name == 'b') { /* #b (binary) */
		x = binary_decode(name + 1);
		return (mk_integer(sc, x));
	} else if (*name == '\\') { /* #\w (character) */
		int c = 0;
		if (strcmp(name + 1, "space") == 0) {
			c = ' ';
		} else if (strcmp(name + 1, "newline") == 0) {
			c = '\n';
		} else if (strcmp(name + 1, "return") == 0) {
			c = '\r';
		} else if (strcmp(name + 1, "tab") == 0) {
			c = '\t';
		} else if (name[1] == 'x' && name[2] != 0) {
			int c1 = 0;
			if (sscanf(name + 2, "%x", (unsigned int *)&c1) == 1 &&
			    c1 < 255) {
				c = c1;
			} else {
				return sc->NIL;
			}
		} else if (is_ascii_name(name + 1, &c)) {
			/* nothing */
		} else if (name[2] == 0) {
			c = name[1];
		} else {
			return sc->NIL;
		}
		return mk_character(sc, c);
	} else
		return (sc->NIL);
}

/* ========== garbage collector ========== */

/*--
 *  We use algorithm E (Knuth, The Art of Computer Programming Vol.1,
 *  sec. 2.3.5), the Schorr-Deutsch-Waite link-inversion algorithm,
 *  for marking.
 */
static void mark(pointer a)
{
	pointer t, q, p;

	t = (pointer)0;
	p = a;
E2:
	setmark(p);
	if (is_vector(p)) {
		int i;
		int num = ivalue_unchecked(p) / 2 + ivalue_unchecked(p) % 2;
		for (i = 0; i < num; i++) {
			/* Vector cells will be treated like ordinary cells */
			mark(p + 1 + i);
		}
	}
	if (is_atom(p))
		goto E6;
	/* E4: down car */
	q = car(p);
	if (q && !is_mark(q)) {
		setatom(p); /* a note that we have moved car */
		car(p) = t;
		t = p;
		p = q;
		goto E2;
	}
E5:
	q = cdr(p); /* down cdr */
	if (q && !is_mark(q)) {
		cdr(p) = t;
		t = p;
		p = q;
		goto E2;
	}
E6: /* up.  Undo the link switching from steps E4 and E5. */
	if (!t)
		return;
	q = t;
	if (is_atom(q)) {
		clratom(q);
		t = car(q);
		car(q) = p;
		p = q;
		goto E5;
	} else {
		t = cdr(q);
		cdr(q) = p;
		p = q;
		goto E6;
	}
}

/* garbage collection. parameter a, b is marked. */
static void gc(scheme *sc, pointer a, pointer b)
{
	pointer p;
	int i;

	if (sc->gc_verbose) {
		putstr(sc, "gc...");
	}

	/* mark system globals */
	mark(sc->oblist);
	mark(sc->global_env);

	/* mark current registers */
	mark(sc->args);
	mark(sc->envir);
	mark(sc->code);
	dump_stack_mark(sc);
	mark(sc->value);
	mark(sc->inport);
	mark(sc->save_inport);
	mark(sc->outport);
	mark(sc->loadport);

	/* Mark recent objects the interpreter doesn't know about yet. */
	mark(car(sc->sink));
	/* Mark any older stuff above nested C calls */
	mark(sc->c_nest);

	/* mark variables a, b */
	mark(a);
	mark(b);

	/* garbage collect */
	clrmark(sc->NIL);
	sc->fcells = 0;
	sc->free_cell = sc->NIL;
	/* free-list is kept sorted by address so as to maintain consecutive
        ranges, if possible, for use with vectors. Here we scan the cells
        (which are also kept sorted by address) downwards to build the
        free-list in sorted order.
     */
	for (i = sc->last_cell_seg; i >= 0; i--) {
		p = sc->cell_seg[i] + CELL_SEGSIZE;
		while (--p >= sc->cell_seg[i]) {
			if (is_mark(p)) {
				clrmark(p);
			} else {
				/* reclaim cell */
				if (typeflag(p) != 0) {
					finalize_cell(sc, p);
					typeflag(p) = 0;
					car(p) = sc->NIL;
				}
				++sc->fcells;
				cdr(p) = sc->free_cell;
				sc->free_cell = p;
			}
		}
	}

	if (sc->gc_verbose) {
		char msg[80];
		snprintf(msg, 80, "done: %ld cells were recovered.\n",
			 sc->fcells);
		putstr(sc, msg);
	}
}

static void finalize_cell(scheme *sc, pointer a)
{
	if (is_string(a)) {
		sc->free(strvalue(a));
	} else if (is_port(a)) {
		if (a->_object._port->kind & port_file &&
		    a->_object._port->rep.stdio.closeit) {
			port_close(sc, a, port_input | port_output);
		}
		sc->free(a->_object._port);
	}
}

/* ========== Routines for Reading ========== */

static int file_push(scheme *sc, const char *fname)
{
	FILE *fin = NULL;

	if (sc->file_i == MAXFIL - 1)
		return 0;
	fin = fopen(fname, "r");
	if (fin != 0) {
		sc->file_i++;
		sc->load_stack[sc->file_i].kind = port_file | port_input;
		sc->load_stack[sc->file_i].rep.stdio.file = fin;
		sc->load_stack[sc->file_i].rep.stdio.closeit = 1;
		sc->nesting_stack[sc->file_i] = 0;
		sc->loadport->_object._port = sc->load_stack + sc->file_i;

#if SHOW_ERROR_LINE
		sc->load_stack[sc->file_i].rep.stdio.curr_line = 0;
		if (fname)
			sc->load_stack[sc->file_i].rep.stdio.filename =
				store_string(sc, strlen(fname), fname, 0);
#endif
	}
	return fin != 0;
}

static void file_pop(scheme *sc)
{
	if (sc->file_i != 0) {
		sc->nesting = sc->nesting_stack[sc->file_i];
		port_close(sc, sc->loadport, port_input);
		sc->file_i--;
		sc->loadport->_object._port = sc->load_stack + sc->file_i;
	}
}

static port *port_rep_from_filename(scheme *sc, const char *fn, int prop)
{
	FILE *f;
	char *rw;
	port *pt;
	if (prop == (port_input | port_output)) {
		rw = "a+";
	} else if (prop == port_output) {
		rw = "w";
	} else {
		rw = "r";
	}
	f = fopen(fn, rw);
	if (f == 0) {
		return 0;
	}
	pt = port_rep_from_file(sc, f, prop);
	pt->rep.stdio.closeit = 1;

#if SHOW_ERROR_LINE
	if (fn)
		pt->rep.stdio.filename = store_string(sc, strlen(fn), fn, 0);

	pt->rep.stdio.curr_line = 0;
#endif
	return pt;
}

static pointer port_from_filename(scheme *sc, const char *fn, int prop)
{
	port *pt;
	pt = port_rep_from_filename(sc, fn, prop);
	if (pt == 0) {
		return sc->NIL;
	}
	return mk_port(sc, pt);
}

static port *port_rep_from_file(scheme *sc, FILE *f, int prop)
{
	port *pt;

	pt = (port *)sc->malloc(sizeof *pt);
	if (pt == NULL) {
		return NULL;
	}
	pt->kind = port_file | prop;
	pt->rep.stdio.file = f;
	pt->rep.stdio.closeit = 0;
	return pt;
}

static pointer port_from_file(scheme *sc, FILE *f, int prop)
{
	port *pt;
	pt = port_rep_from_file(sc, f, prop);
	if (pt == 0) {
		return sc->NIL;
	}
	return mk_port(sc, pt);
}

static port *port_rep_from_string(scheme *sc, char *start, char *past_the_end,
				  int prop)
{
	port *pt;
	pt = (port *)sc->malloc(sizeof(port));
	if (pt == 0) {
		return 0;
	}
	pt->kind = port_string | prop;
	pt->rep.string.start = start;
	pt->rep.string.curr = start;
	pt->rep.string.past_the_end = past_the_end;
	return pt;
}

static pointer port_from_string(scheme *sc, char *start, char *past_the_end,
				int prop)
{
	port *pt;
	pt = port_rep_from_string(sc, start, past_the_end, prop);
	if (pt == 0) {
		return sc->NIL;
	}
	return mk_port(sc, pt);
}

#define BLOCK_SIZE 256

static port *port_rep_from_scratch(scheme *sc)
{
	port *pt;
	char *start;
	pt = (port *)sc->malloc(sizeof(port));
	if (pt == 0) {
		return 0;
	}
	start = sc->malloc(BLOCK_SIZE);
	if (start == 0) {
		return 0;
	}
	memset(start, ' ', BLOCK_SIZE - 1);
	start[BLOCK_SIZE - 1] = '\0';
	pt->kind = port_string | port_output | port_srfi6;
	pt->rep.string.start = start;
	pt->rep.string.curr = start;
	pt->rep.string.past_the_end = start + BLOCK_SIZE - 1;
	return pt;
}

static pointer port_from_scratch(scheme *sc)
{
	port *pt;
	pt = port_rep_from_scratch(sc);
	if (pt == 0) {
		return sc->NIL;
	}
	return mk_port(sc, pt);
}

static void port_close(scheme *sc, pointer p, int flag)
{
	port *pt = p->_object._port;
	pt->kind &= ~flag;
	if ((pt->kind & (port_input | port_output)) == 0) {
		if (pt->kind & port_file) {
#if SHOW_ERROR_LINE
			/* Cleanup is here so (close-*-port) functions could work too */
			pt->rep.stdio.curr_line = 0;

			if (pt->rep.stdio.filename)
				sc->free(pt->rep.stdio.filename);
#endif

			fclose(pt->rep.stdio.file);
		}
		pt->kind = port_free;
	}
}

/* get new character from input file */
static int inchar(scheme *sc)
{
	int c;
	port *pt;

	pt = sc->inport->_object._port;
	if (pt->kind & port_saw_EOF) {
		return EOF;
	}
	c = basic_inchar(pt);
	if (c == EOF && sc->inport == sc->loadport) {
		/* Instead, set port_saw_EOF */
		pt->kind |= port_saw_EOF;

		/* file_pop(sc); */
		return EOF;
		/* NOTREACHED */
	}
	return c;
}

static int basic_inchar(port *pt)
{
	if (pt->kind & port_file) {
		return fgetc(pt->rep.stdio.file);
	} else {
		if (*pt->rep.string.curr == 0 ||
		    pt->rep.string.curr == pt->rep.string.past_the_end) {
			return EOF;
		} else {
			return *pt->rep.string.curr++;
		}
	}
}

/* back character to input buffer */
static void backchar(scheme *sc, int c)
{
	port *pt;
	if (c == EOF)
		return;
	pt = sc->inport->_object._port;
	if (pt->kind & port_file) {
		ungetc(c, pt->rep.stdio.file);
	} else {
		if (pt->rep.string.curr != pt->rep.string.start) {
			--pt->rep.string.curr;
		}
	}
}

static int realloc_port_string(scheme *sc, port *p)
{
	char *start = p->rep.string.start;
	size_t new_size = p->rep.string.past_the_end - start + 1 + BLOCK_SIZE;
	char *str = sc->malloc(new_size);
	if (str) {
		memset(str, ' ', new_size - 1);
		str[new_size - 1] = '\0';
		strcpy(str, start);
		p->rep.string.start = str;
		p->rep.string.past_the_end = str + new_size - 1;
		p->rep.string.curr -= start - str;
		sc->free(start);
		return 1;
	} else {
		return 0;
	}
}

void putstr(scheme *sc, const char *s)
{
	port *pt = sc->outport->_object._port;
	if (pt->kind & port_file) {
		fputs(s, pt->rep.stdio.file);
	} else {
		for (; *s; s++) {
			if (pt->rep.string.curr !=
			    pt->rep.string.past_the_end) {
				*pt->rep.string.curr++ = *s;
			} else if (pt->kind & port_srfi6 &&
				   realloc_port_string(sc, pt)) {
				*pt->rep.string.curr++ = *s;
			}
		}
	}
}

static void putchars(scheme *sc, const char *s, int len)
{
	port *pt = sc->outport->_object._port;
	if (pt->kind & port_file) {
		fwrite(s, 1, len, pt->rep.stdio.file);
	} else {
		for (; len; len--) {
			if (pt->rep.string.curr !=
			    pt->rep.string.past_the_end) {
				*pt->rep.string.curr++ = *s++;
			} else if (pt->kind & port_srfi6 &&
				   realloc_port_string(sc, pt)) {
				*pt->rep.string.curr++ = *s++;
			}
		}
	}
}

void putcharacter(scheme *sc, int c)
{
	port *pt = sc->outport->_object._port;
	if (pt->kind & port_file) {
		fputc(c, pt->rep.stdio.file);
	} else {
		if (pt->rep.string.curr != pt->rep.string.past_the_end) {
			*pt->rep.string.curr++ = c;
		} else if (pt->kind & port_srfi6 &&
			   realloc_port_string(sc, pt)) {
			*pt->rep.string.curr++ = c;
		}
	}
}

/* read characters up to delimiter, but cater to character constants */
static char *readstr_upto(scheme *sc, char *delim)
{
	char *p = sc->strbuff;

	while ((p - sc->strbuff < sizeof(sc->strbuff)) &&
	       !is_one_of(delim, (*p++ = inchar(sc))))
		;

	if (p == sc->strbuff + 2 && p[-2] == '\\') {
		*p = 0;
	} else {
		backchar(sc, p[-1]);
		*--p = '\0';
	}
	return sc->strbuff;
}

/* read string expression "xxx...xxx" */
static pointer readstrexp(scheme *sc)
{
	char *p = sc->strbuff;
	int c;
	int c1 = 0;
	enum { st_ok, st_bsl, st_x1, st_x2, st_oct1, st_oct2 } state = st_ok;

	for (;;) {
		c = inchar(sc);
		if (c == EOF || p - sc->strbuff > sizeof(sc->strbuff) - 1) {
			return sc->F;
		}
		switch (state) {
		case st_ok:
			switch (c) {
			case '\\':
				state = st_bsl;
				break;
			case '"':
				*p = 0;
				return mk_counted_string(sc, sc->strbuff,
							 p - sc->strbuff);
			default:
				*p++ = c;
				break;
			}
			break;
		case st_bsl:
			switch (c) {
			case '0':
			case '1':
			case '2':
			case '3':
			case '4':
			case '5':
			case '6':
			case '7':
				state = st_oct1;
				c1 = c - '0';
				break;
			case 'x':
			case 'X':
				state = st_x1;
				c1 = 0;
				break;
			case 'n':
				*p++ = '\n';
				state = st_ok;
				break;
			case 't':
				*p++ = '\t';
				state = st_ok;
				break;
			case 'r':
				*p++ = '\r';
				state = st_ok;
				break;
			case '"':
				*p++ = '"';
				state = st_ok;
				break;
			default:
				*p++ = c;
				state = st_ok;
				break;
			}
			break;
		case st_x1:
		case st_x2:
			c = toupper(c);
			if (c >= '0' && c <= 'F') {
				if (c <= '9') {
					c1 = (c1 << 4) + c - '0';
				} else {
					c1 = (c1 << 4) + c - 'A' + 10;
				}
				if (state == st_x1) {
					state = st_x2;
				} else {
					*p++ = c1;
					state = st_ok;
				}
			} else {
				return sc->F;
			}
			break;
		case st_oct1:
		case st_oct2:
			if (c < '0' || c > '7') {
				*p++ = c1;
				backchar(sc, c);
				state = st_ok;
			} else {
				if (state == st_oct2 && c1 >= 32)
					return sc->F;

				c1 = (c1 << 3) + (c - '0');

				if (state == st_oct1)
					state = st_oct2;
				else {
					*p++ = c1;
					state = st_ok;
				}
			}
			break;
		}
	}
}

/* check c is in chars */
static int is_one_of(char *s, int c)
{
	if (c == EOF)
		return 1;
	while (*s)
		if (*s++ == c)
			return (1);
	return (0);
}

/* skip white characters */
static int skipspace(scheme *sc)
{
	int c = 0, curr_line = 0;

	do {
		c = inchar(sc);
#if SHOW_ERROR_LINE
		if (c == '\n')
			curr_line++;
#endif
	} while (isspace(c));

/* record it */
#if SHOW_ERROR_LINE
	if (sc->load_stack[sc->file_i].kind & port_file)
		sc->load_stack[sc->file_i].rep.stdio.curr_line += curr_line;
#endif

	if (c != EOF) {
		backchar(sc, c);
		return 1;
	} else {
		return EOF;
	}
}

/* get token */
static int token(scheme *sc)
{
	int c;
	c = skipspace(sc);
	if (c == EOF) {
		return (TOK_EOF);
	}
	switch (c = inchar(sc)) {
	case EOF:
		return (TOK_EOF);
	case '(':
		return (TOK_LPAREN);
	case ')':
		return (TOK_RPAREN);
	case '.':
		c = inchar(sc);
		if (is_one_of(" \n\t", c)) {
			return (TOK_DOT);
		} else {
			backchar(sc, c);
			backchar(sc, '.');
			return TOK_ATOM;
		}
	case '\'':
		return (TOK_QUOTE);
	case ';':
		while ((c = inchar(sc)) != '\n' && c != EOF)
			;

#if SHOW_ERROR_LINE
		if (c == '\n' && sc->load_stack[sc->file_i].kind & port_file)
			sc->load_stack[sc->file_i].rep.stdio.curr_line++;
#endif

		if (c == EOF) {
			return (TOK_EOF);
		} else {
			return (token(sc));
		}
	case '"':
		return (TOK_DQUOTE);
	case BACKQUOTE:
		return (TOK_BQUOTE);
	case ',':
		if ((c = inchar(sc)) == '@') {
			return (TOK_ATMARK);
		} else {
			backchar(sc, c);
			return (TOK_COMMA);
		}
	case '#':
		c = inchar(sc);
		if (c == '(') {
			return (TOK_VEC);
		} else if (c == '!') {
			while ((c = inchar(sc)) != '\n' && c != EOF)
				;

#if SHOW_ERROR_LINE
			if (c == '\n' &&
			    sc->load_stack[sc->file_i].kind & port_file)
				sc->load_stack[sc->file_i].rep.stdio.curr_line++;
#endif

			if (c == EOF) {
				return (TOK_EOF);
			} else {
				return (token(sc));
			}
		} else {
			backchar(sc, c);
			if (is_one_of(" tfodxb\\", c)) {
				return TOK_SHARP_CONST;
			} else {
				return (TOK_SHARP);
			}
		}
	default:
		backchar(sc, c);
		return (TOK_ATOM);
	}
}

/* ========== Routines for Printing ========== */
#define ok_abbrev(x) (is_pair(x) && cdr(x) == sc->NIL)

static void printslashstring(scheme *sc, char *p, int len)
{
	int i;
	unsigned char *s = (unsigned char *)p;
	putcharacter(sc, '"');
	for (i = 0; i < len; i++) {
		if (*s == 0xff || *s == '"' || *s < ' ' || *s == '\\') {
			putcharacter(sc, '\\');
			switch (*s) {
			case '"':
				putcharacter(sc, '"');
				break;
			case '\n':
				putcharacter(sc, 'n');
				break;
			case '\t':
				putcharacter(sc, 't');
				break;
			case '\r':
				putcharacter(sc, 'r');
				break;
			case '\\':
				putcharacter(sc, '\\');
				break;
			default: {
				int d = *s / 16;
				putcharacter(sc, 'x');
				if (d < 10) {
					putcharacter(sc, d + '0');
				} else {
					putcharacter(sc, d - 10 + 'A');
				}
				d = *s % 16;
				if (d < 10) {
					putcharacter(sc, d + '0');
				} else {
					putcharacter(sc, d - 10 + 'A');
				}
			}
			}
		} else {
			putcharacter(sc, *s);
		}
		s++;
	}
	putcharacter(sc, '"');
}

/* print atoms */
static void printatom(scheme *sc, pointer l, int f)
{
	char *p;
	int len;
	atom2str(sc, l, f, &p, &len);
	putchars(sc, p, len);
}

/* Uses internal buffer unless string pointer is already available */
static void atom2str(scheme *sc, pointer l, int f, char **pp, int *plen)
{
	char *p;

	if (l == sc->NIL) {
		p = "()";
	} else if (l == sc->T) {
		p = "#t";
	} else if (l == sc->F) {
		p = "#f";
	} else if (l == sc->EOF_OBJ) {
		p = "#<EOF>";
	} else if (is_port(l)) {
		p = "#<PORT>";
	} else if (is_number(l)) {
		p = sc->strbuff;
		if (f <= 1 || f == 10) /* f is the base for numbers if > 1 */
		{
			if (num_is_integer(l)) {
				snprintf(p, STRBUFFSIZE, "%ld",
					 ivalue_unchecked(l));
			} else {
				snprintf(p, STRBUFFSIZE, "%.10g",
					 rvalue_unchecked(l));
				/* r5rs says there must be a '.' (unless 'e'?) */
				f = strcspn(p, ".e");
				if (p[f] == 0) {
					p[f] = '.'; /* not found, so add '.0' at the end */
					p[f + 1] = '0';
					p[f + 2] = 0;
				}
			}
		} else {
			long v = ivalue(l);
			if (f == 16) {
				if (v >= 0)
					snprintf(p, STRBUFFSIZE, "%lx", v);
				else
					snprintf(p, STRBUFFSIZE, "-%lx", -v);
			} else if (f == 8) {
				if (v >= 0)
					snprintf(p, STRBUFFSIZE, "%lo", v);
				else
					snprintf(p, STRBUFFSIZE, "-%lo", -v);
			} else if (f == 2) {
				unsigned long b = (v < 0) ? -v : v;
				p = &p[STRBUFFSIZE - 1];
				*p = 0;
				do {
					*--p = (b & 1) ? '1' : '0';
					b >>= 1;
				} while (b != 0);
				if (v < 0)
					*--p = '-';
			}
		}
	} else if (is_string(l)) {
		if (!f) {
			p = strvalue(l);
		} else { /* Hack, uses the fact that printing is needed */
			*pp = sc->strbuff;
			*plen = 0;
			printslashstring(sc, strvalue(l), strlength(l));
			return;
		}
	} else if (is_character(l)) {
		int c = charvalue(l);
		p = sc->strbuff;
		if (!f) {
			p[0] = c;
			p[1] = 0;
		} else {
			switch (c) {
			case ' ':
				p = "#\\space";
				break;
			case '\n':
				p = "#\\newline";
				break;
			case '\r':
				p = "#\\return";
				break;
			case '\t':
				p = "#\\tab";
				break;
			default:
#if USE_ASCII_NAMES
				if (c == 127) {
					p = "#\\del";
					break;
				} else if (c < 32) {
					snprintf(p, STRBUFFSIZE, "#\\%s",
						 charnames[c]);
					break;
				}
#else
				if (c < 32) {
					snprintf(p, STRBUFFSIZE, "#\\x%x", c);
					break;
				}
#endif
				snprintf(p, STRBUFFSIZE, "#\\%c", c);
				break;
			}
		}
	} else if (is_symbol(l)) {
		p = symname(l);
	} else if (is_proc(l)) {
		p = sc->strbuff;
		snprintf(p, STRBUFFSIZE, "#<%s PROCEDURE %ld>", procname(l),
			 procnum(l));
	} else if (is_macro(l)) {
		p = "#<MACRO>";
	} else if (is_closure(l)) {
		p = "#<CLOSURE>";
	} else if (is_promise(l)) {
		p = "#<PROMISE>";
	} else if (is_foreign(l)) {
		p = sc->strbuff;
		snprintf(p, STRBUFFSIZE, "#<FOREIGN PROCEDURE %ld>",
			 procnum(l));
	} else if (is_continuation(l)) {
		p = "#<CONTINUATION>";
	} else {
		p = "#<ERROR>";
	}
	*pp = p;
	*plen = strlen(p);
}
/* ========== Routines for Evaluation Cycle ========== */

/* make closure. c is code. e is environment */
static pointer mk_closure(scheme *sc, pointer c, pointer e)
{
	pointer x = get_cell(sc, c, e);

	typeflag(x) = T_CLOSURE;
	car(x) = c;
	cdr(x) = e;
	return (x);
}

/* make continuation. */
static pointer mk_continuation(scheme *sc, pointer d)
{
	pointer x = get_cell(sc, sc->NIL, d);

	typeflag(x) = T_CONTINUATION;
	cont_dump(x) = d;
	return (x);
}

static pointer list_star(scheme *sc, pointer d)
{
	pointer p, q;
	if (cdr(d) == sc->NIL) {
		return car(d);
	}
	p = cons(sc, car(d), cdr(d));
	q = p;
	while (cdr(cdr(p)) != sc->NIL) {
		d = cons(sc, car(p), cdr(p));
		if (cdr(cdr(p)) != sc->NIL) {
			p = cdr(d);
		}
	}
	cdr(p) = car(cdr(p));
	return q;
}

/* reverse list -- produce new list */
static pointer reverse(scheme *sc, pointer a)
{
	/* a must be checked by gc */
	pointer p = sc->NIL;

	for (; is_pair(a); a = cdr(a)) {
		p = cons(sc, car(a), p);
	}
	return (p);
}

/* reverse list --- in-place */
static pointer reverse_in_place(scheme *sc, pointer term, pointer list)
{
	pointer p = list, result = term, q;

	while (p != sc->NIL) {
		q = cdr(p);
		cdr(p) = result;
		result = p;
		p = q;
	}
	return (result);
}

/* append list -- produce new list (in reverse order) */
static pointer revappend(scheme *sc, pointer a, pointer b)
{
	pointer result = a;
	pointer p = b;

	while (is_pair(p)) {
		result = cons(sc, car(p), result);
		p = cdr(p);
	}

	if (p == sc->NIL) {
		return result;
	}

	return sc->F; /* signal an error */
}

/* equivalence of atoms */
int eqv(pointer a, pointer b)
{
	if (is_string(a)) {
		if (is_string(b))
			return (strvalue(a) == strvalue(b));
		else
			return (0);
	} else if (is_number(a)) {
		if (is_number(b)) {
			if (num_is_integer(a) == num_is_integer(b))
				return num_eq(nvalue(a), nvalue(b));
		}
		return (0);
	} else if (is_character(a)) {
		if (is_character(b))
			return charvalue(a) == charvalue(b);
		else
			return (0);
	} else if (is_port(a)) {
		if (is_port(b))
			return a == b;
		else
			return (0);
	} else if (is_proc(a)) {
		if (is_proc(b))
			return procnum(a) == procnum(b);
		else
			return (0);
	} else {
		return (a == b);
	}
}

/* true or false value macro */
/* () is #t in R5RS */
#define is_true(p) ((p) != sc->F)
#define is_false(p) ((p) == sc->F)

/* ========== Environment implementation  ========== */

#if !defined(USE_ALIST_ENV) || !defined(USE_OBJECT_LIST)

static int hash_fn(const char *key, int table_size)
{
	unsigned int hashed = 0;
	const char *c;
	int bits_per_int = sizeof(unsigned int) * 8;

	for (c = key; *c; c++) {
		/* letters have about 5 bits in them */
		hashed = (hashed << 5) | (hashed >> (bits_per_int - 5));
		hashed ^= *c;
	}
	return hashed % table_size;
}
#endif

#ifndef USE_ALIST_ENV

/*
 * In this implementation, each frame of the environment may be
 * a hash table: a vector of alists hashed by variable name.
 * In practice, we use a vector only for the initial frame;
 * subsequent frames are too small and transient for the lookup
 * speed to out-weigh the cost of making a new vector.
 */

static void new_frame_in_env(scheme *sc, pointer old_env)
{
	pointer new_frame;

	/* The interaction-environment has about 300 variables in it. */
	if (old_env == sc->NIL) {
		new_frame = mk_vector(sc, 461);
	} else {
		new_frame = sc->NIL;
	}

	sc->envir = immutable_cons(sc, new_frame, old_env);
	setenvironment(sc->envir);
}

static void new_slot_spec_in_env(scheme *sc, pointer env, pointer variable,
				 pointer value)
{
	pointer slot = immutable_cons(sc, variable, value);

	if (is_vector(car(env))) {
		int location =
			hash_fn(symname(variable), ivalue_unchecked(car(env)));

		set_vector_elem(
			car(env), location,
			immutable_cons(sc, slot,
				       vector_elem(car(env), location)));
	} else {
		car(env) = immutable_cons(sc, slot, car(env));
	}
}

static pointer find_slot_in_env(scheme *sc, pointer env, pointer hdl, int all)
{
	pointer x, y;
	int location;

	for (x = env; x != sc->NIL; x = cdr(x)) {
		if (is_vector(car(x))) {
			location =
				hash_fn(symname(hdl), ivalue_unchecked(car(x)));
			y = vector_elem(car(x), location);
		} else {
			y = car(x);
		}
		for (; y != sc->NIL; y = cdr(y)) {
			if (caar(y) == hdl) {
				break;
			}
		}
		if (y != sc->NIL) {
			break;
		}
		if (!all) {
			return sc->NIL;
		}
	}
	if (x != sc->NIL) {
		return car(y);
	}
	return sc->NIL;
}

#else /* USE_ALIST_ENV */

static void new_frame_in_env(scheme *sc, pointer old_env)
{
	sc->envir = immutable_cons(sc, sc->NIL, old_env);
	setenvironment(sc->envir);
}

static void new_slot_spec_in_env(scheme *sc, pointer env, pointer variable,
				 pointer value)
{
	car(env) = immutable_cons(sc, immutable_cons(sc, variable, value),
				  car(env));
}

static pointer find_slot_in_env(scheme *sc, pointer env, pointer hdl, int all)
{
	pointer x, y;
	for (x = env; x != sc->NIL; x = cdr(x)) {
		for (y = car(x); y != sc->NIL; y = cdr(y)) {
			if (caar(y) == hdl) {
				break;
			}
		}
		if (y != sc->NIL) {
			break;
		}
		if (!all) {
			return sc->NIL;
		}
	}
	if (x != sc->NIL) {
		return car(y);
	}
	return sc->NIL;
}

#endif /* USE_ALIST_ENV else */

static void new_slot_in_env(scheme *sc, pointer variable, pointer value)
{
	new_slot_spec_in_env(sc, sc->envir, variable, value);
}

static void set_slot_in_env(scheme *sc, pointer slot, pointer value)
{
	cdr(slot) = value;
}

static pointer slot_value_in_env(pointer slot)
{
	return cdr(slot);
}

/* ========== Evaluation Cycle ========== */

static pointer _Error_1(scheme *sc, const char *s, pointer a)
{
	const char *str = s;
#if USE_ERROR_HOOK
	pointer x;
	pointer hdl = sc->ERROR_HOOK;
#endif

#if SHOW_ERROR_LINE
	char sbuf[STRBUFFSIZE];

	/* make sure error is not in REPL */
	if (sc->load_stack[sc->file_i].kind & port_file &&
	    sc->load_stack[sc->file_i].rep.stdio.file != stdin) {
		int ln = sc->load_stack[sc->file_i].rep.stdio.curr_line;
		const char *fname =
			sc->load_stack[sc->file_i].rep.stdio.filename;

		/* should never happen */
		if (!fname)
			fname = "<unknown>";

		/* we started from 0 */
		ln++;
		snprintf(sbuf, STRBUFFSIZE, "(%s : %i) %s", fname, ln, s);

		str = (const char *)sbuf;
	}
#endif

#if USE_ERROR_HOOK
	x = find_slot_in_env(sc, sc->envir, hdl, 1);
	if (x != sc->NIL) {
		if (a != 0) {
			sc->code = cons(
				sc, cons(sc, sc->QUOTE, cons(sc, (a), sc->NIL)),
				sc->NIL);
		} else {
			sc->code = sc->NIL;
		}
		sc->code = cons(sc, mk_string(sc, str), sc->code);
		setimmutable(car(sc->code));
		sc->code = cons(sc, slot_value_in_env(x), sc->code);
		sc->op = (int)OP_EVAL;
		return sc->T;
	}
#endif

	if (a != 0) {
		sc->args = cons(sc, (a), sc->NIL);
	} else {
		sc->args = sc->NIL;
	}
	sc->args = cons(sc, mk_string(sc, str), sc->args);
	setimmutable(car(sc->args));
	sc->op = (int)OP_ERR0;
	return sc->T;
}
#define Error_1(sc, s, a) return _Error_1(sc, s, a)
#define Error_0(sc, s) return _Error_1(sc, s, 0)

/* Too small to turn into function */
#define BEGIN do {
#define END                                                                    \
	}                                                                      \
	while (0)
#define s_goto(sc, a)                                                          \
	BEGIN                                                                  \
	sc->op = (int)(a);                                                     \
	return sc->T;                                                          \
	END

#define s_return(sc, a) return _s_return(sc, a)

static void dump_stack_reset(scheme *sc)
{
	sc->dump = sc->NIL;
}

static void dump_stack_initialize(scheme *sc)
{
	dump_stack_reset(sc);
}

static void dump_stack_free(scheme *sc)
{
	sc->dump = sc->NIL;
}

static pointer _s_return(scheme *sc, pointer a)
{
	sc->value = (a);
	if (sc->dump == sc->NIL)
		return sc->NIL;
	sc->op = ivalue(car(sc->dump));
	sc->args = cadr(sc->dump);
	sc->envir = caddr(sc->dump);
	sc->code = cadddr(sc->dump);
	sc->dump = cddddr(sc->dump);
	return sc->T;
}

static void s_save(scheme *sc, enum scheme_opcodes op, pointer args,
		   pointer code)
{
	sc->dump = cons(sc, sc->envir, cons(sc, (code), sc->dump));
	sc->dump = cons(sc, (args), sc->dump);
	sc->dump = cons(sc, mk_integer(sc, (long)(op)), sc->dump);
}

static void dump_stack_mark(scheme *sc)
{
	mark(sc->dump);
}

#define s_retbool(tf) s_return(sc, (tf) ? sc->T : sc->F)

static pointer opexe_0(scheme *sc, enum scheme_opcodes op)
{
	pointer x, y;

	switch (op) {
	case OP_LOAD: /* load */
		if (!file_push(sc, strvalue(car(sc->args)))) {
			Error_1(sc, "unable to open", car(sc->args));
		} else {
			sc->args = mk_integer(sc, sc->file_i);
			s_goto(sc, OP_T0LVL);
		}

	case OP_T0LVL: /* top level */
		/* If we reached the end of file, this loop is done. */
		if (sc->loadport->_object._port->kind & port_saw_EOF) {
			if (sc->file_i == 0) {
				sc->args = sc->NIL;
				s_goto(sc, OP_QUIT);
			} else {
				file_pop(sc);
				s_return(sc, sc->value);
			}
			/* NOTREACHED */
		}

		/* Set up another iteration of REPL */
		sc->nesting = 0;
		sc->save_inport = sc->inport;
		sc->inport = sc->loadport;
		s_save(sc, OP_T0LVL, sc->NIL, sc->NIL);
		s_save(sc, OP_VALUEPRINT, sc->NIL, sc->NIL);
		s_save(sc, OP_T1LVL, sc->NIL, sc->NIL);
		s_goto(sc, OP_READ_INTERNAL);

	case OP_T1LVL: /* top level */
		sc->code = sc->value;
		sc->inport = sc->save_inport;
		s_goto(sc, OP_EVAL);

	case OP_READ_INTERNAL: /* internal read */
		sc->tok = token(sc);
		if (sc->tok == TOK_EOF) {
			s_return(sc, sc->EOF_OBJ);
		}
		s_goto(sc, OP_RDSEXPR);

	case OP_GENSYM:
		s_return(sc, gensym(sc));

	case OP_VALUEPRINT: /* print evaluation result */
		if (sc->tracing) {
			putstr(sc, "\nGives: ");
		}
		s_return(sc, sc->value);

	case OP_EVAL: /* main part of evaluation */
#if USE_TRACING
		if (sc->tracing) {
			/*s_save(sc,OP_VALUEPRINT,sc->NIL,sc->NIL);*/
			s_save(sc, OP_REAL_EVAL, sc->args, sc->code);
			sc->args = sc->code;
			putstr(sc, "\nEval: ");
			s_goto(sc, OP_P0LIST);
		}
		/* fall through */
	case OP_REAL_EVAL:
#endif
		if (is_symbol(sc->code)) { /* symbol */
			x = find_slot_in_env(sc, sc->envir, sc->code, 1);
			if (x != sc->NIL) {
				s_return(sc, slot_value_in_env(x));
			} else {
				Error_1(sc,
					"eval: unbound variable:", sc->code);
			}
		} else if (is_pair(sc->code)) {
			if (is_syntax(x = car(sc->code))) { /* SYNTAX */
				sc->code = cdr(sc->code);
				s_goto(sc, syntaxnum(x));
			} else { /* first, eval top element and eval arguments */
				s_save(sc, OP_E0ARGS, sc->NIL, sc->code);
				/* If no macros => s_save(sc,OP_E1ARGS, sc->NIL, cdr(sc->code));*/
				sc->code = car(sc->code);
				s_goto(sc, OP_EVAL);
			}
		} else {
			s_return(sc, sc->code);
		}

	case OP_E0ARGS: /* eval arguments */
		if (is_macro(sc->value)) { /* macro expansion */
			s_save(sc, OP_DOMACRO, sc->NIL, sc->NIL);
			sc->args = cons(sc, sc->code, sc->NIL);
			sc->code = sc->value;
			s_goto(sc, OP_APPLY);
		} else {
			sc->code = cdr(sc->code);
			s_goto(sc, OP_E1ARGS);
		}

	case OP_E1ARGS: /* eval arguments */
		sc->args = cons(sc, sc->value, sc->args);
		if (is_pair(sc->code)) { /* continue */
			s_save(sc, OP_E1ARGS, sc->args, cdr(sc->code));
			sc->code = car(sc->code);
			sc->args = sc->NIL;
			s_goto(sc, OP_EVAL);
		} else { /* end */
			sc->args = reverse_in_place(sc, sc->NIL, sc->args);
			sc->code = car(sc->args);
			sc->args = cdr(sc->args);
			s_goto(sc, OP_APPLY);
		}

#if USE_TRACING
	case OP_TRACING: {
		int tr = sc->tracing;
		sc->tracing = ivalue(car(sc->args));
		s_return(sc, mk_integer(sc, tr));
	}
#endif

	case OP_APPLY: /* apply 'code' to 'args' */
#if USE_TRACING
		if (sc->tracing) {
			s_save(sc, OP_REAL_APPLY, sc->args, sc->code);
			sc->print_flag = 1;
			/*  sc->args=cons(sc,sc->code,sc->args);*/
			putstr(sc, "\nApply to: ");
			s_goto(sc, OP_P0LIST);
		}
		/* fall through */
	case OP_REAL_APPLY:
#endif
		if (is_proc(sc->code)) {
			s_goto(sc, procnum(sc->code)); /* PROCEDURE */
		} else if (is_foreign(sc->code)) {
			/* Keep nested calls from GC'ing the arglist */
			push_recent_alloc(sc, sc->args, sc->NIL);
			x = sc->code->_object._ff(sc, sc->args);
			s_return(sc, x);
		} else if (is_closure(sc->code) || is_macro(sc->code) ||
			   is_promise(sc->code)) { /* CLOSURE */
			/* Should not accept promise */
			/* make environment */
			new_frame_in_env(sc, closure_env(sc->code));
			for (x = car(closure_code(sc->code)), y = sc->args;
			     is_pair(x); x = cdr(x), y = cdr(y)) {
				if (y == sc->NIL) {
					Error_0(sc, "not enough arguments");
				} else {
					new_slot_in_env(sc, car(x), car(y));
				}
			}
			if (x == sc->NIL) {
				/*--
                     * if (y != sc->NIL) {
                     *   Error_0(sc,"too many arguments");
                     * }
                     */
			} else if (is_symbol(x))
				new_slot_in_env(sc, x, y);
			else {
				Error_1(sc,
					"syntax error in closure: not a symbol:",
					x);
			}
			sc->code = cdr(closure_code(sc->code));
			sc->args = sc->NIL;
			s_goto(sc, OP_BEGIN);
		} else if (is_continuation(sc->code)) { /* CONTINUATION */
			sc->dump = cont_dump(sc->code);
			s_return(sc,
				 sc->args != sc->NIL ? car(sc->args) : sc->NIL);
		} else {
			Error_0(sc, "illegal function");
		}

	case OP_DOMACRO: /* do macro */
		sc->code = sc->value;
		s_goto(sc, OP_EVAL);

#if 1
	case OP_LAMBDA: /* lambda */
		/* If the hook is defined, apply it to sc->code, otherwise
             set sc->value fall thru */
		{
			pointer f = find_slot_in_env(sc, sc->envir,
						     sc->COMPILE_HOOK, 1);
			if (f == sc->NIL) {
				sc->value = sc->code;
				/* Fallthru */
			} else {
				s_save(sc, OP_LAMBDA1, sc->args, sc->code);
				sc->args = cons(sc, sc->code, sc->NIL);
				sc->code = slot_value_in_env(f);
				s_goto(sc, OP_APPLY);
			}
		}

	case OP_LAMBDA1:
		s_return(sc, mk_closure(sc, sc->value, sc->envir));

#else
	case OP_LAMBDA: /* lambda */
		s_return(sc, mk_closure(sc, sc->code, sc->envir));

#endif

	case OP_MKCLOSURE: /* make-closure */
		x = car(sc->args);
		if (car(x) == sc->LAMBDA) {
			x = cdr(x);
		}
		if (cdr(sc->args) == sc->NIL) {
			y = sc->envir;
		} else {
			y = cadr(sc->args);
		}
		s_return(sc, mk_closure(sc, x, y));

	case OP_QUOTE: /* quote */
		s_return(sc, car(sc->code));

	case OP_DEF0: /* define */
		if (is_immutable(car(sc->code)))
			Error_1(sc, "define: unable to alter immutable",
				car(sc->code));

		if (is_pair(car(sc->code))) {
			x = caar(sc->code);
			sc->code =
				cons(sc, sc->LAMBDA,
				     cons(sc, cdar(sc->code), cdr(sc->code)));
		} else {
			x = car(sc->code);
			sc->code = cadr(sc->code);
		}
		if (!is_symbol(x)) {
			Error_0(sc, "variable is not a symbol");
		}
		s_save(sc, OP_DEF1, sc->NIL, x);
		s_goto(sc, OP_EVAL);

	case OP_DEF1: /* define */
		x = find_slot_in_env(sc, sc->envir, sc->code, 0);
		if (x != sc->NIL) {
			set_slot_in_env(sc, x, sc->value);
		} else {
			new_slot_in_env(sc, sc->code, sc->value);
		}
		s_return(sc, sc->code);

	case OP_DEFP: /* defined? */
		x = sc->envir;
		if (cdr(sc->args) != sc->NIL) {
			x = cadr(sc->args);
		}
		s_retbool(find_slot_in_env(sc, x, car(sc->args), 1) != sc->NIL);

	case OP_SET0: /* set! */
		if (is_immutable(car(sc->code)))
			Error_1(sc, "set!: unable to alter immutable variable",
				car(sc->code));
		s_save(sc, OP_SET1, sc->NIL, car(sc->code));
		sc->code = cadr(sc->code);
		s_goto(sc, OP_EVAL);

	case OP_SET1: /* set! */
		y = find_slot_in_env(sc, sc->envir, sc->code, 1);
		if (y != sc->NIL) {
			set_slot_in_env(sc, y, sc->value);
			s_return(sc, sc->value);
		} else {
			Error_1(sc, "set!: unbound variable:", sc->code);
		}

	case OP_BEGIN: /* begin */
		if (!is_pair(sc->code)) {
			s_return(sc, sc->code);
		}
		if (cdr(sc->code) != sc->NIL) {
			s_save(sc, OP_BEGIN, sc->NIL, cdr(sc->code));
		}
		sc->code = car(sc->code);
		s_goto(sc, OP_EVAL);

	case OP_IF0: /* if */
		s_save(sc, OP_IF1, sc->NIL, cdr(sc->code));
		sc->code = car(sc->code);
		s_goto(sc, OP_EVAL);

	case OP_IF1: /* if */
		if (is_true(sc->value))
			sc->code = car(sc->code);
		else
			sc->code = cadr(sc->code); /* (if #f 1) ==> () because
                                           * car(sc->NIL) = sc->NIL */
		s_goto(sc, OP_EVAL);

	case OP_LET0: /* let */
		sc->args = sc->NIL;
		sc->value = sc->code;
		sc->code = is_symbol(car(sc->code)) ? cadr(sc->code) :
							    car(sc->code);
		s_goto(sc, OP_LET1);

	case OP_LET1: /* let (calculate parameters) */
		sc->args = cons(sc, sc->value, sc->args);
		if (is_pair(sc->code)) { /* continue */
			if (!is_pair(car(sc->code)) ||
			    !is_pair(cdar(sc->code))) {
				Error_1(sc,
					"Bad syntax of binding spec in let :",
					car(sc->code));
			}
			s_save(sc, OP_LET1, sc->args, cdr(sc->code));
			sc->code = cadar(sc->code);
			sc->args = sc->NIL;
			s_goto(sc, OP_EVAL);
		} else { /* end */
			sc->args = reverse_in_place(sc, sc->NIL, sc->args);
			sc->code = car(sc->args);
			sc->args = cdr(sc->args);
			s_goto(sc, OP_LET2);
		}

	case OP_LET2: /* let */
		new_frame_in_env(sc, sc->envir);
		for (x = is_symbol(car(sc->code)) ? cadr(sc->code) :
							  car(sc->code),
		    y = sc->args;
		     y != sc->NIL; x = cdr(x), y = cdr(y)) {
			new_slot_in_env(sc, caar(x), car(y));
		}
		if (is_symbol(car(sc->code))) { /* named let */
			for (x = cadr(sc->code), sc->args = sc->NIL;
			     x != sc->NIL; x = cdr(x)) {
				if (!is_pair(x))
					Error_1(sc,
						"Bad syntax of binding in let :",
						x);
				if (!is_list(sc, car(x)))
					Error_1(sc,
						"Bad syntax of binding in let :",
						car(x));
				sc->args = cons(sc, caar(x), sc->args);
			}
			x = mk_closure(
				sc,
				cons(sc,
				     reverse_in_place(sc, sc->NIL, sc->args),
				     cddr(sc->code)),
				sc->envir);
			new_slot_in_env(sc, car(sc->code), x);
			sc->code = cddr(sc->code);
			sc->args = sc->NIL;
		} else {
			sc->code = cdr(sc->code);
			sc->args = sc->NIL;
		}
		s_goto(sc, OP_BEGIN);

	case OP_LET0AST: /* let* */
		if (car(sc->code) == sc->NIL) {
			new_frame_in_env(sc, sc->envir);
			sc->code = cdr(sc->code);
			s_goto(sc, OP_BEGIN);
		}
		if (!is_pair(car(sc->code)) || !is_pair(caar(sc->code)) ||
		    !is_pair(cdaar(sc->code))) {
			Error_1(sc, "Bad syntax of binding spec in let* :",
				car(sc->code));
		}
		s_save(sc, OP_LET1AST, cdr(sc->code), car(sc->code));
		sc->code = cadaar(sc->code);
		s_goto(sc, OP_EVAL);

	case OP_LET1AST: /* let* (make new frame) */
		new_frame_in_env(sc, sc->envir);
		s_goto(sc, OP_LET2AST);

	case OP_LET2AST: /* let* (calculate parameters) */
		new_slot_in_env(sc, caar(sc->code), sc->value);
		sc->code = cdr(sc->code);
		if (is_pair(sc->code)) { /* continue */
			s_save(sc, OP_LET2AST, sc->args, sc->code);
			sc->code = cadar(sc->code);
			sc->args = sc->NIL;
			s_goto(sc, OP_EVAL);
		} else { /* end */
			sc->code = sc->args;
			sc->args = sc->NIL;
			s_goto(sc, OP_BEGIN);
		}
	default:
		snprintf(sc->strbuff, STRBUFFSIZE, "%d: illegal operator",
			 sc->op);
		Error_0(sc, sc->strbuff);
	}
	return sc->T;
}

static pointer opexe_1(scheme *sc, enum scheme_opcodes op)
{
	pointer x, y;

	switch (op) {
	case OP_LET0REC: /* letrec */
		new_frame_in_env(sc, sc->envir);
		sc->args = sc->NIL;
		sc->value = sc->code;
		sc->code = car(sc->code);
		s_goto(sc, OP_LET1REC);

	case OP_LET1REC: /* letrec (calculate parameters) */
		sc->args = cons(sc, sc->value, sc->args);
		if (is_pair(sc->code)) { /* continue */
			if (!is_pair(car(sc->code)) ||
			    !is_pair(cdar(sc->code))) {
				Error_1(sc,
					"Bad syntax of binding spec in letrec :",
					car(sc->code));
			}
			s_save(sc, OP_LET1REC, sc->args, cdr(sc->code));
			sc->code = cadar(sc->code);
			sc->args = sc->NIL;
			s_goto(sc, OP_EVAL);
		} else { /* end */
			sc->args = reverse_in_place(sc, sc->NIL, sc->args);
			sc->code = car(sc->args);
			sc->args = cdr(sc->args);
			s_goto(sc, OP_LET2REC);
		}

	case OP_LET2REC: /* letrec */
		for (x = car(sc->code), y = sc->args; y != sc->NIL;
		     x = cdr(x), y = cdr(y)) {
			new_slot_in_env(sc, caar(x), car(y));
		}
		sc->code = cdr(sc->code);
		sc->args = sc->NIL;
		s_goto(sc, OP_BEGIN);

	case OP_COND0: /* cond */
		if (!is_pair(sc->code)) {
			Error_0(sc, "syntax error in cond");
		}
		s_save(sc, OP_COND1, sc->NIL, sc->code);
		sc->code = caar(sc->code);
		s_goto(sc, OP_EVAL);

	case OP_COND1: /* cond */
		if (is_true(sc->value)) {
			if ((sc->code = cdar(sc->code)) == sc->NIL) {
				s_return(sc, sc->value);
			}
			if (!sc->code || car(sc->code) == sc->FEED_TO) {
				if (!is_pair(cdr(sc->code))) {
					Error_0(sc, "syntax error in cond");
				}
				x = cons(sc, sc->QUOTE,
					 cons(sc, sc->value, sc->NIL));
				sc->code = cons(sc, cadr(sc->code),
						cons(sc, x, sc->NIL));
				s_goto(sc, OP_EVAL);
			}
			s_goto(sc, OP_BEGIN);
		} else {
			if ((sc->code = cdr(sc->code)) == sc->NIL) {
				s_return(sc, sc->NIL);
			} else {
				s_save(sc, OP_COND1, sc->NIL, sc->code);
				sc->code = caar(sc->code);
				s_goto(sc, OP_EVAL);
			}
		}

	case OP_DELAY: /* delay */
		x = mk_closure(sc, cons(sc, sc->NIL, sc->code), sc->envir);
		typeflag(x) = T_PROMISE;
		s_return(sc, x);

	case OP_AND0: /* and */
		if (sc->code == sc->NIL) {
			s_return(sc, sc->T);
		}
		s_save(sc, OP_AND1, sc->NIL, cdr(sc->code));
		sc->code = car(sc->code);
		s_goto(sc, OP_EVAL);

	case OP_AND1: /* and */
		if (is_false(sc->value)) {
			s_return(sc, sc->value);
		} else if (sc->code == sc->NIL) {
			s_return(sc, sc->value);
		} else {
			s_save(sc, OP_AND1, sc->NIL, cdr(sc->code));
			sc->code = car(sc->code);
			s_goto(sc, OP_EVAL);
		}

	case OP_OR0: /* or */
		if (sc->code == sc->NIL) {
			s_return(sc, sc->F);
		}
		s_save(sc, OP_OR1, sc->NIL, cdr(sc->code));
		sc->code = car(sc->code);
		s_goto(sc, OP_EVAL);

	case OP_OR1: /* or */
		if (is_true(sc->value)) {
			s_return(sc, sc->value);
		} else if (sc->code == sc->NIL) {
			s_return(sc, sc->value);
		} else {
			s_save(sc, OP_OR1, sc->NIL, cdr(sc->code));
			sc->code = car(sc->code);
			s_goto(sc, OP_EVAL);
		}

	case OP_C0STREAM: /* cons-stream */
		s_save(sc, OP_C1STREAM, sc->NIL, cdr(sc->code));
		sc->code = car(sc->code);
		s_goto(sc, OP_EVAL);

	case OP_C1STREAM: /* cons-stream */
		sc->args =
			sc->value; /* save sc->value to register sc->args for gc */
		x = mk_closure(sc, cons(sc, sc->NIL, sc->code), sc->envir);
		typeflag(x) = T_PROMISE;
		s_return(sc, cons(sc, sc->args, x));

	case OP_MACRO0: /* macro */
		if (is_pair(car(sc->code))) {
			x = caar(sc->code);
			sc->code =
				cons(sc, sc->LAMBDA,
				     cons(sc, cdar(sc->code), cdr(sc->code)));
		} else {
			x = car(sc->code);
			sc->code = cadr(sc->code);
		}
		if (!is_symbol(x)) {
			Error_0(sc, "variable is not a symbol");
		}
		s_save(sc, OP_MACRO1, sc->NIL, x);
		s_goto(sc, OP_EVAL);

	case OP_MACRO1: /* macro */
		typeflag(sc->value) = T_MACRO;
		x = find_slot_in_env(sc, sc->envir, sc->code, 0);
		if (x != sc->NIL) {
			set_slot_in_env(sc, x, sc->value);
		} else {
			new_slot_in_env(sc, sc->code, sc->value);
		}
		s_return(sc, sc->code);

	case OP_CASE0: /* case */
		s_save(sc, OP_CASE1, sc->NIL, cdr(sc->code));
		sc->code = car(sc->code);
		s_goto(sc, OP_EVAL);

	case OP_CASE1: /* case */
		for (x = sc->code; x != sc->NIL; x = cdr(x)) {
			if (!is_pair(y = caar(x))) {
				break;
			}
			for (; y != sc->NIL; y = cdr(y)) {
				if (eqv(car(y), sc->value)) {
					break;
				}
			}
			if (y != sc->NIL) {
				break;
			}
		}
		if (x != sc->NIL) {
			if (is_pair(caar(x))) {
				sc->code = cdar(x);
				s_goto(sc, OP_BEGIN);
			} else { /* else */
				s_save(sc, OP_CASE2, sc->NIL, cdar(x));
				sc->code = caar(x);
				s_goto(sc, OP_EVAL);
			}
		} else {
			s_return(sc, sc->NIL);
		}

	case OP_CASE2: /* case */
		if (is_true(sc->value)) {
			s_goto(sc, OP_BEGIN);
		} else {
			s_return(sc, sc->NIL);
		}

	case OP_PAPPLY: /* apply */
		sc->code = car(sc->args);
		sc->args = list_star(sc, cdr(sc->args));
		/*sc->args = cadr(sc->args);*/
		s_goto(sc, OP_APPLY);

	case OP_PEVAL: /* eval */
		if (cdr(sc->args) != sc->NIL) {
			sc->envir = cadr(sc->args);
		}
		sc->code = car(sc->args);
		s_goto(sc, OP_EVAL);

	case OP_CONTINUATION: /* call-with-current-continuation */
		sc->code = car(sc->args);
		sc->args = cons(sc, mk_continuation(sc, sc->dump), sc->NIL);
		s_goto(sc, OP_APPLY);

	default:
		snprintf(sc->strbuff, STRBUFFSIZE, "%d: illegal operator",
			 sc->op);
		Error_0(sc, sc->strbuff);
	}
	return sc->T;
}

static pointer opexe_2(scheme *sc, enum scheme_opcodes op)
{
	pointer x;
	num v;
#if USE_MATH
	double dd;
#endif

	switch (op) {
#if USE_MATH
	case OP_INEX2EX: /* inexact->exact */
		x = car(sc->args);
		if (num_is_integer(x)) {
			s_return(sc, x);
		} else if (modf(rvalue_unchecked(x), &dd) == 0.0) {
			s_return(sc, mk_integer(sc, ivalue(x)));
		} else {
			Error_1(sc, "inexact->exact: not integral:", x);
		}

	case OP_EXP:
		x = car(sc->args);
		s_return(sc, mk_real(sc, exp(rvalue(x))));

	case OP_LOG:
		x = car(sc->args);
		s_return(sc, mk_real(sc, log(rvalue(x))));

	case OP_SIN:
		x = car(sc->args);
		s_return(sc, mk_real(sc, sin(rvalue(x))));

	case OP_COS:
		x = car(sc->args);
		s_return(sc, mk_real(sc, cos(rvalue(x))));

	case OP_TAN:
		x = car(sc->args);
		s_return(sc, mk_real(sc, tan(rvalue(x))));

	case OP_ASIN:
		x = car(sc->args);
		s_return(sc, mk_real(sc, asin(rvalue(x))));

	case OP_ACOS:
		x = car(sc->args);
		s_return(sc, mk_real(sc, acos(rvalue(x))));

	case OP_ATAN:
		x = car(sc->args);
		if (cdr(sc->args) == sc->NIL) {
			s_return(sc, mk_real(sc, atan(rvalue(x))));
		} else {
			pointer y = cadr(sc->args);
			s_return(sc, mk_real(sc, atan2(rvalue(x), rvalue(y))));
		}

	case OP_SQRT:
		x = car(sc->args);
		s_return(sc, mk_real(sc, sqrt(rvalue(x))));

	case OP_EXPT: {
		double result;
		int real_result = 1;
		pointer y = cadr(sc->args);
		x = car(sc->args);
		if (num_is_integer(x) && num_is_integer(y))
			real_result = 0;
		/* This 'if' is an R5RS compatibility fix. */
		/* NOTE: Remove this 'if' fix for R6RS.    */
		if (rvalue(x) == 0 && rvalue(y) < 0) {
			result = 0.0;
		} else {
			result = pow(rvalue(x), rvalue(y));
		}
		/* Before returning integer result make sure we can. */
		/* If the test fails, result is too big for integer. */
		if (!real_result) {
			long result_as_long = (long)result;
			if (result != (double)result_as_long)
				real_result = 1;
		}
		if (real_result) {
			s_return(sc, mk_real(sc, result));
		} else {
			s_return(sc, mk_integer(sc, result));
		}
	}

	case OP_FLOOR:
		x = car(sc->args);
		s_return(sc, mk_real(sc, floor(rvalue(x))));

	case OP_CEILING:
		x = car(sc->args);
		s_return(sc, mk_real(sc, ceil(rvalue(x))));

	case OP_TRUNCATE: {
		double rvalue_of_x;
		x = car(sc->args);
		rvalue_of_x = rvalue(x);
		if (rvalue_of_x > 0) {
			s_return(sc, mk_real(sc, floor(rvalue_of_x)));
		} else {
			s_return(sc, mk_real(sc, ceil(rvalue_of_x)));
		}
	}

	case OP_ROUND:
		x = car(sc->args);
		if (num_is_integer(x))
			s_return(sc, x);
		s_return(sc, mk_real(sc, round_per_R5RS(rvalue(x))));
#endif

	case OP_ADD: /* + */
		v = num_zero;
		for (x = sc->args; x != sc->NIL; x = cdr(x)) {
			v = num_add(v, nvalue(car(x)));
		}
		s_return(sc, mk_number(sc, v));

	case OP_MUL: /* * */
		v = num_one;
		for (x = sc->args; x != sc->NIL; x = cdr(x)) {
			v = num_mul(v, nvalue(car(x)));
		}
		s_return(sc, mk_number(sc, v));

	case OP_SUB: /* - */
		if (cdr(sc->args) == sc->NIL) {
			x = sc->args;
			v = num_zero;
		} else {
			x = cdr(sc->args);
			v = nvalue(car(sc->args));
		}
		for (; x != sc->NIL; x = cdr(x)) {
			v = num_sub(v, nvalue(car(x)));
		}
		s_return(sc, mk_number(sc, v));

	case OP_DIV: /* / */
		if (cdr(sc->args) == sc->NIL) {
			x = sc->args;
			v = num_one;
		} else {
			x = cdr(sc->args);
			v = nvalue(car(sc->args));
		}
		for (; x != sc->NIL; x = cdr(x)) {
			if (!is_zero_double(rvalue(car(x))))
				v = num_div(v, nvalue(car(x)));
			else {
				Error_0(sc, "/: division by zero");
			}
		}
		s_return(sc, mk_number(sc, v));

	case OP_INTDIV: /* quotient */
		if (cdr(sc->args) == sc->NIL) {
			x = sc->args;
			v = num_one;
		} else {
			x = cdr(sc->args);
			v = nvalue(car(sc->args));
		}
		for (; x != sc->NIL; x = cdr(x)) {
			if (ivalue(car(x)) != 0)
				v = num_intdiv(v, nvalue(car(x)));
			else {
				Error_0(sc, "quotient: division by zero");
			}
		}
		s_return(sc, mk_number(sc, v));

	case OP_REM: /* remainder */
		v = nvalue(car(sc->args));
		if (ivalue(cadr(sc->args)) != 0)
			v = num_rem(v, nvalue(cadr(sc->args)));
		else {
			Error_0(sc, "remainder: division by zero");
		}
		s_return(sc, mk_number(sc, v));

	case OP_MOD: /* modulo */
		v = nvalue(car(sc->args));
		if (ivalue(cadr(sc->args)) != 0)
			v = num_mod(v, nvalue(cadr(sc->args)));
		else {
			Error_0(sc, "modulo: division by zero");
		}
		s_return(sc, mk_number(sc, v));

	case OP_CAR: /* car */
		s_return(sc, caar(sc->args));

	case OP_CDR: /* cdr */
		s_return(sc, cdar(sc->args));

	case OP_CONS: /* cons */
		cdr(sc->args) = cadr(sc->args);
		s_return(sc, sc->args);

	case OP_SETCAR: /* set-car! */
		if (!is_immutable(car(sc->args))) {
			caar(sc->args) = cadr(sc->args);
			s_return(sc, car(sc->args));
		} else {
			Error_0(sc, "set-car!: unable to alter immutable pair");
		}

	case OP_SETCDR: /* set-cdr! */
		if (!is_immutable(car(sc->args))) {
			cdar(sc->args) = cadr(sc->args);
			s_return(sc, car(sc->args));
		} else {
			Error_0(sc, "set-cdr!: unable to alter immutable pair");
		}

	case OP_CHAR2INT: { /* char->integer */
		char c;
		c = (char)ivalue(car(sc->args));
		s_return(sc, mk_integer(sc, (unsigned char)c));
	}

	case OP_INT2CHAR: { /* integer->char */
		unsigned char c;
		c = (unsigned char)ivalue(car(sc->args));
		s_return(sc, mk_character(sc, (char)c));
	}

	case OP_CHARUPCASE: {
		unsigned char c;
		c = (unsigned char)ivalue(car(sc->args));
		c = toupper(c);
		s_return(sc, mk_character(sc, (char)c));
	}

	case OP_CHARDNCASE: {
		unsigned char c;
		c = (unsigned char)ivalue(car(sc->args));
		c = tolower(c);
		s_return(sc, mk_character(sc, (char)c));
	}

	case OP_STR2SYM: /* string->symbol */
		s_return(sc, mk_symbol(sc, strvalue(car(sc->args))));

	case OP_STR2ATOM: /* string->atom */
	{
		char *s = strvalue(car(sc->args));
		long pf = 0;
		if (cdr(sc->args) != sc->NIL) {
			/* we know cadr(sc->args) is a natural number */
			/* see if it is 2, 8, 10, or 16, or error */
			pf = ivalue_unchecked(cadr(sc->args));
			if (pf == 16 || pf == 10 || pf == 8 || pf == 2) {
				/* base is OK */
			} else {
				pf = -1;
			}
		}
		if (pf < 0) {
			Error_1(sc, "string->atom: bad base:", cadr(sc->args));
		} else if (*s == '#') /* no use of base! */
		{
			s_return(sc, mk_sharp_const(sc, s + 1));
		} else {
			if (pf == 0 || pf == 10) {
				s_return(sc, mk_atom(sc, s));
			} else {
				char *ep;
				long iv = strtol(s, &ep, (int)pf);
				if (*ep == 0) {
					s_return(sc, mk_integer(sc, iv));
				} else {
					s_return(sc, sc->F);
				}
			}
		}
	}

	case OP_SYM2STR: /* symbol->string */
		x = mk_string(sc, symname(car(sc->args)));
		setimmutable(x);
		s_return(sc, x);

	case OP_ATOM2STR: /* atom->string */
	{
		long pf = 0;
		x = car(sc->args);
		if (cdr(sc->args) != sc->NIL) {
			/* we know cadr(sc->args) is a natural number */
			/* see if it is 2, 8, 10, or 16, or error */
			pf = ivalue_unchecked(cadr(sc->args));
			if (is_number(x) &&
			    (pf == 16 || pf == 10 || pf == 8 || pf == 2)) {
				/* base is OK */
			} else {
				pf = -1;
			}
		}
		if (pf < 0) {
			Error_1(sc, "atom->string: bad base:", cadr(sc->args));
		} else if (is_number(x) || is_character(x) || is_string(x) ||
			   is_symbol(x)) {
			char *p;
			int len;
			atom2str(sc, x, (int)pf, &p, &len);
			s_return(sc, mk_counted_string(sc, p, len));
		} else {
			Error_1(sc, "atom->string: not an atom:", x);
		}
	}

	case OP_MKSTRING: { /* make-string */
		int fill = ' ';
		int len;

		len = ivalue(car(sc->args));

		if (cdr(sc->args) != sc->NIL) {
			fill = charvalue(cadr(sc->args));
		}
		s_return(sc, mk_empty_string(sc, len, (char)fill));
	}

	case OP_STRLEN: /* string-length */
		s_return(sc, mk_integer(sc, strlength(car(sc->args))));

	case OP_STRREF: { /* string-ref */
		char *str;
		int index;

		str = strvalue(car(sc->args));

		index = ivalue(cadr(sc->args));

		if (index >= strlength(car(sc->args))) {
			Error_1(sc,
				"string-ref: out of bounds:", cadr(sc->args));
		}

		s_return(sc, mk_character(sc, ((unsigned char *)str)[index]));
	}

	case OP_STRSET: { /* string-set! */
		char *str;
		int index;
		int c;

		if (is_immutable(car(sc->args))) {
			Error_1(sc,
				"string-set!: unable to alter immutable string:",
				car(sc->args));
		}
		str = strvalue(car(sc->args));

		index = ivalue(cadr(sc->args));
		if (index >= strlength(car(sc->args))) {
			Error_1(sc,
				"string-set!: out of bounds:", cadr(sc->args));
		}

		c = charvalue(caddr(sc->args));

		str[index] = (char)c;
		s_return(sc, car(sc->args));
	}

	case OP_STRAPPEND: { /* string-append */
		/* in 1.29 string-append was in Scheme in init.scm but was too slow */
		int len = 0;
		pointer newstr;
		char *pos;

		/* compute needed length for new string */
		for (x = sc->args; x != sc->NIL; x = cdr(x)) {
			len += strlength(car(x));
		}
		newstr = mk_empty_string(sc, len, ' ');
		/* store the contents of the argument strings into the new string */
		for (pos = strvalue(newstr), x = sc->args; x != sc->NIL;
		     pos += strlength(car(x)), x = cdr(x)) {
			memcpy(pos, strvalue(car(x)), strlength(car(x)));
		}
		s_return(sc, newstr);
	}

	case OP_SUBSTR: { /* substring */
		char *str;
		int index0;
		int index1;
		int len;

		str = strvalue(car(sc->args));

		index0 = ivalue(cadr(sc->args));

		if (index0 > strlength(car(sc->args))) {
			Error_1(sc, "substring: start out of bounds:",
				cadr(sc->args));
		}

		if (cddr(sc->args) != sc->NIL) {
			index1 = ivalue(caddr(sc->args));
			if (index1 > strlength(car(sc->args)) ||
			    index1 < index0) {
				Error_1(sc, "substring: end out of bounds:",
					caddr(sc->args));
			}
		} else {
			index1 = strlength(car(sc->args));
		}

		len = index1 - index0;
		x = mk_empty_string(sc, len, ' ');
		memcpy(strvalue(x), str + index0, len);
		strvalue(x)[len] = 0;

		s_return(sc, x);
	}

	case OP_VECTOR: { /* vector */
		int i;
		pointer vec;
		int len = list_length(sc, sc->args);
		if (len < 0) {
			Error_1(sc, "vector: not a proper list:", sc->args);
		}
		vec = mk_vector(sc, len);
		if (sc->no_memory) {
			s_return(sc, sc->sink);
		}
		for (x = sc->args, i = 0; is_pair(x); x = cdr(x), i++) {
			set_vector_elem(vec, i, car(x));
		}
		s_return(sc, vec);
	}

	case OP_MKVECTOR: { /* make-vector */
		pointer fill = sc->NIL;
		int len;
		pointer vec;

		len = ivalue(car(sc->args));

		if (cdr(sc->args) != sc->NIL) {
			fill = cadr(sc->args);
		}
		vec = mk_vector(sc, len);
		if (sc->no_memory) {
			s_return(sc, sc->sink);
		}
		if (fill != sc->NIL) {
			fill_vector(vec, fill);
		}
		s_return(sc, vec);
	}

	case OP_VECLEN: /* vector-length */
		s_return(sc, mk_integer(sc, ivalue(car(sc->args))));

	case OP_VECREF: { /* vector-ref */
		int index;

		index = ivalue(cadr(sc->args));

		if (index >= ivalue(car(sc->args))) {
			Error_1(sc,
				"vector-ref: out of bounds:", cadr(sc->args));
		}

		s_return(sc, vector_elem(car(sc->args), index));
	}

	case OP_VECSET: { /* vector-set! */
		int index;

		if (is_immutable(car(sc->args))) {
			Error_1(sc,
				"vector-set!: unable to alter immutable vector:",
				car(sc->args));
		}

		index = ivalue(cadr(sc->args));
		if (index >= ivalue(car(sc->args))) {
			Error_1(sc,
				"vector-set!: out of bounds:", cadr(sc->args));
		}

		set_vector_elem(car(sc->args), index, caddr(sc->args));
		s_return(sc, car(sc->args));
	}

	default:
		snprintf(sc->strbuff, STRBUFFSIZE, "%d: illegal operator",
			 sc->op);
		Error_0(sc, sc->strbuff);
	}
	return sc->T;
}

static int is_list(scheme *sc, pointer a)
{
	return list_length(sc, a) >= 0;
}

/* Result is:
   proper list: length
   circular list: -1
   not even a pair: -2
   dotted list: -2 minus length before dot
*/
int list_length(scheme *sc, pointer a)
{
	int i = 0;
	pointer slow, fast;

	slow = fast = a;
	while (1) {
		if (fast == sc->NIL)
			return i;
		if (!is_pair(fast))
			return -2 - i;
		fast = cdr(fast);
		++i;
		if (fast == sc->NIL)
			return i;
		if (!is_pair(fast))
			return -2 - i;
		++i;
		fast = cdr(fast);

		/* Safe because we would have already returned if `fast'
             encountered a non-pair. */
		slow = cdr(slow);
		if (fast == slow) {
			/* the fast pointer has looped back around and caught up
                  with the slow pointer, hence the structure is circular,
                  not of finite length, and therefore not a list */
			return -1;
		}
	}
}

static pointer opexe_3(scheme *sc, enum scheme_opcodes op)
{
	pointer x;
	num v;
	int (*comp_func)(num, num) = 0;

	switch (op) {
	case OP_NOT: /* not */
		s_retbool(is_false(car(sc->args)));
	case OP_BOOLP: /* boolean? */
		s_retbool(car(sc->args) == sc->F || car(sc->args) == sc->T);
	case OP_EOFOBJP: /* boolean? */
		s_retbool(car(sc->args) == sc->EOF_OBJ);
	case OP_NULLP: /* null? */
		s_retbool(car(sc->args) == sc->NIL);
	case OP_NUMEQ: /* = */
	case OP_LESS: /* < */
	case OP_GRE: /* > */
	case OP_LEQ: /* <= */
	case OP_GEQ: /* >= */
		switch (op) {
		case OP_NUMEQ:
			comp_func = num_eq;
			break;
		case OP_LESS:
			comp_func = num_lt;
			break;
		case OP_GRE:
			comp_func = num_gt;
			break;
		case OP_LEQ:
			comp_func = num_le;
			break;
		case OP_GEQ:
			comp_func = num_ge;
			break;
		default:
			break;
		}
		x = sc->args;
		v = nvalue(car(x));
		x = cdr(x);

		for (; x != sc->NIL; x = cdr(x)) {
			if (!comp_func(v, nvalue(car(x)))) {
				s_retbool(0);
			}
			v = nvalue(car(x));
		}
		s_retbool(1);
	case OP_SYMBOLP: /* symbol? */
		s_retbool(is_symbol(car(sc->args)));
	case OP_NUMBERP: /* number? */
		s_retbool(is_number(car(sc->args)));
	case OP_STRINGP: /* string? */
		s_retbool(is_string(car(sc->args)));
	case OP_INTEGERP: /* integer? */
		s_retbool(is_integer(car(sc->args)));
	case OP_REALP: /* real? */
		s_retbool(is_number(car(sc->args))); /* All numbers are real */
	case OP_CHARP: /* char? */
		s_retbool(is_character(car(sc->args)));
	case OP_CHARAP: /* char-alphabetic? */
		s_retbool(Cisalpha(ivalue(car(sc->args))));
	case OP_CHARNP: /* char-numeric? */
		s_retbool(Cisdigit(ivalue(car(sc->args))));
	case OP_CHARWP: /* char-whitespace? */
		s_retbool(Cisspace(ivalue(car(sc->args))));
	case OP_CHARUP: /* char-upper-case? */
		s_retbool(Cisupper(ivalue(car(sc->args))));
	case OP_CHARLP: /* char-lower-case? */
		s_retbool(Cislower(ivalue(car(sc->args))));
	case OP_PORTP: /* port? */
		s_retbool(is_port(car(sc->args)));
	case OP_INPORTP: /* input-port? */
		s_retbool(is_inport(car(sc->args)));
	case OP_OUTPORTP: /* output-port? */
		s_retbool(is_outport(car(sc->args)));
	case OP_PROCP: /* procedure? */
		/*--
           * continuation should be procedure by the example
           * (call-with-current-continuation procedure?) ==> #t
           * in R^3 report sec. 6.9
           */
		s_retbool(is_proc(car(sc->args)) || is_closure(car(sc->args)) ||
			  is_continuation(car(sc->args)) ||
			  is_foreign(car(sc->args)));
	case OP_PAIRP: /* pair? */
		s_retbool(is_pair(car(sc->args)));
	case OP_LISTP: /* list? */
		s_retbool(list_length(sc, car(sc->args)) >= 0);

	case OP_ENVP: /* environment? */
		s_retbool(is_environment(car(sc->args)));
	case OP_VECTORP: /* vector? */
		s_retbool(is_vector(car(sc->args)));
	case OP_EQ: /* eq? */
		s_retbool(car(sc->args) == cadr(sc->args));
	case OP_EQV: /* eqv? */
		s_retbool(eqv(car(sc->args), cadr(sc->args)));
	default:
		snprintf(sc->strbuff, STRBUFFSIZE, "%d: illegal operator",
			 sc->op);
		Error_0(sc, sc->strbuff);
	}
	return sc->T;
}

static pointer opexe_4(scheme *sc, enum scheme_opcodes op)
{
	pointer x, y;

	switch (op) {
	case OP_FORCE: /* force */
		sc->code = car(sc->args);
		if (is_promise(sc->code)) {
			/* Should change type to closure here */
			s_save(sc, OP_SAVE_FORCED, sc->NIL, sc->code);
			sc->args = sc->NIL;
			s_goto(sc, OP_APPLY);
		} else {
			s_return(sc, sc->code);
		}

	case OP_SAVE_FORCED: /* Save forced value replacing promise */
		memcpy(sc->code, sc->value, sizeof(struct cell));
		s_return(sc, sc->value);

	case OP_WRITE: /* write */
	case OP_DISPLAY: /* display */
	case OP_WRITE_CHAR: /* write-char */
		if (is_pair(cdr(sc->args))) {
			if (cadr(sc->args) != sc->outport) {
				x = cons(sc, sc->outport, sc->NIL);
				s_save(sc, OP_SET_OUTPORT, x, sc->NIL);
				sc->outport = cadr(sc->args);
			}
		}
		sc->args = car(sc->args);
		if (op == OP_WRITE) {
			sc->print_flag = 1;
		} else {
			sc->print_flag = 0;
		}
		s_goto(sc, OP_P0LIST);

	case OP_NEWLINE: /* newline */
		if (is_pair(sc->args)) {
			if (car(sc->args) != sc->outport) {
				x = cons(sc, sc->outport, sc->NIL);
				s_save(sc, OP_SET_OUTPORT, x, sc->NIL);
				sc->outport = car(sc->args);
			}
		}
		putstr(sc, "\n");
		s_return(sc, sc->T);

	case OP_ERR0: /* error */
		sc->retcode = -1;
		if (!is_string(car(sc->args))) {
			sc->args = cons(sc, mk_string(sc, " -- "), sc->args);
			setimmutable(car(sc->args));
		}
		putstr(sc, "Error: ");
		putstr(sc, strvalue(car(sc->args)));
		sc->args = cdr(sc->args);
		s_goto(sc, OP_ERR1);

	case OP_ERR1: /* error */
		putstr(sc, " ");
		if (sc->args != sc->NIL) {
			s_save(sc, OP_ERR1, cdr(sc->args), sc->NIL);
			sc->args = car(sc->args);
			sc->print_flag = 1;
			s_goto(sc, OP_P0LIST);
		} else {
			putstr(sc, "\n");
			return sc->NIL;
		}

	case OP_REVERSE: /* reverse */
		s_return(sc, reverse(sc, car(sc->args)));

	case OP_LIST_STAR: /* list* */
		s_return(sc, list_star(sc, sc->args));

	case OP_APPEND: /* append */
		x = sc->NIL;
		y = sc->args;
		if (y == x) {
			s_return(sc, x);
		}

		/* cdr() in the while condition is not a typo. If car() */
		/* is used (append '() 'a) will return the wrong result.*/
		while (cdr(y) != sc->NIL) {
			x = revappend(sc, x, car(y));
			y = cdr(y);
			if (x == sc->F) {
				Error_0(sc, "non-list argument to append");
			}
		}

		s_return(sc, reverse_in_place(sc, car(y), x));
	case OP_QUIT: /* quit */
		if (is_pair(sc->args)) {
			sc->retcode = ivalue(car(sc->args));
		}
		return (sc->NIL);

	case OP_GC: /* gc */
		gc(sc, sc->NIL, sc->NIL);
		s_return(sc, sc->T);

	case OP_GCVERB: /* gc-verbose */
	{
		int was = sc->gc_verbose;

		sc->gc_verbose = (car(sc->args) != sc->F);
		s_retbool(was);
	}

	case OP_NEWSEGMENT: /* new-segment */
		if (!is_pair(sc->args) || !is_number(car(sc->args))) {
			Error_0(sc, "new-segment: argument must be a number");
		}
		alloc_cellseg(sc, (int)ivalue(car(sc->args)));
		s_return(sc, sc->T);

	case OP_OBLIST: /* oblist */
		s_return(sc, oblist_all_symbols(sc));

	case OP_CURR_INPORT: /* current-input-port */
		s_return(sc, sc->inport);

	case OP_CURR_OUTPORT: /* current-output-port */
		s_return(sc, sc->outport);

	case OP_OPEN_INFILE: /* open-input-file */
	case OP_OPEN_OUTFILE: /* open-output-file */
	case OP_OPEN_INOUTFILE: /* open-input-output-file */
	{
		int prop = 0;
		pointer p;
		switch (op) {
		case OP_OPEN_INFILE:
			prop = port_input;
			break;
		case OP_OPEN_OUTFILE:
			prop = port_output;
			break;
		case OP_OPEN_INOUTFILE:
			prop = port_input | port_output;
			break;
		default:
			break;
		}
		p = port_from_filename(sc, strvalue(car(sc->args)), prop);
		if (p == sc->NIL) {
			s_return(sc, sc->F);
		}
		s_return(sc, p);
	default:
		break;
	}

#if USE_STRING_PORTS
	case OP_OPEN_INSTRING: /* open-input-string */
	case OP_OPEN_INOUTSTRING: /* open-input-output-string */
	{
		int prop = 0;
		pointer p;
		switch (op) {
		case OP_OPEN_INSTRING:
			prop = port_input;
			break;
		case OP_OPEN_INOUTSTRING:
			prop = port_input | port_output;
			break;
		default:
			break;
		}
		p = port_from_string(sc, strvalue(car(sc->args)),
				     strvalue(car(sc->args)) +
					     strlength(car(sc->args)),
				     prop);
		if (p == sc->NIL) {
			s_return(sc, sc->F);
		}
		s_return(sc, p);
	}
	case OP_OPEN_OUTSTRING: /* open-output-string */
	{
		pointer p;
		if (car(sc->args) == sc->NIL) {
			p = port_from_scratch(sc);
			if (p == sc->NIL) {
				s_return(sc, sc->F);
			}
		} else {
			p = port_from_string(sc, strvalue(car(sc->args)),
					     strvalue(car(sc->args)) +
						     strlength(car(sc->args)),
					     port_output);
			if (p == sc->NIL) {
				s_return(sc, sc->F);
			}
		}
		s_return(sc, p);
	}
	case OP_GET_OUTSTRING: /* get-output-string */
	{
		port *p;

		if ((p = car(sc->args)->_object._port)->kind & port_string) {
			off_t size;
			char *str;

			size = p->rep.string.curr - p->rep.string.start + 1;
			str = sc->malloc(size);
			if (str != NULL) {
				pointer s;

				memcpy(str, p->rep.string.start, size - 1);
				str[size - 1] = '\0';
				s = mk_string(sc, str);
				sc->free(str);
				s_return(sc, s);
			}
		}
		s_return(sc, sc->F);
	}
#endif

	case OP_CLOSE_INPORT: /* close-input-port */
		port_close(sc, car(sc->args), port_input);
		s_return(sc, sc->T);

	case OP_CLOSE_OUTPORT: /* close-output-port */
		port_close(sc, car(sc->args), port_output);
		s_return(sc, sc->T);

	case OP_INT_ENV: /* interaction-environment */
		s_return(sc, sc->global_env);

	case OP_CURR_ENV: /* current-environment */
		s_return(sc, sc->envir);
	}
	return sc->T;
}

static pointer opexe_5(scheme *sc, enum scheme_opcodes op)
{
	pointer x;

	if (sc->nesting != 0) {
		int n = sc->nesting;
		sc->nesting = 0;
		sc->retcode = -1;
		Error_1(sc, "unmatched parentheses:", mk_integer(sc, n));
	}

	switch (op) {
	/* ========== reading part ========== */
	case OP_READ:
		if (!is_pair(sc->args)) {
			s_goto(sc, OP_READ_INTERNAL);
		}
		if (!is_inport(car(sc->args))) {
			Error_1(sc, "read: not an input port:", car(sc->args));
		}
		if (car(sc->args) == sc->inport) {
			s_goto(sc, OP_READ_INTERNAL);
		}
		x = sc->inport;
		sc->inport = car(sc->args);
		x = cons(sc, x, sc->NIL);
		s_save(sc, OP_SET_INPORT, x, sc->NIL);
		s_goto(sc, OP_READ_INTERNAL);

	case OP_READ_CHAR: /* read-char */
	case OP_PEEK_CHAR: /* peek-char */
	{
		int c;
		if (is_pair(sc->args)) {
			if (car(sc->args) != sc->inport) {
				x = sc->inport;
				x = cons(sc, x, sc->NIL);
				s_save(sc, OP_SET_INPORT, x, sc->NIL);
				sc->inport = car(sc->args);
			}
		}
		c = inchar(sc);
		if (c == EOF) {
			s_return(sc, sc->EOF_OBJ);
		}
		if (sc->op == OP_PEEK_CHAR) {
			backchar(sc, c);
		}
		s_return(sc, mk_character(sc, c));
	}

	case OP_CHAR_READY: /* char-ready? */
	{
		pointer p = sc->inport;
		int res;
		if (is_pair(sc->args)) {
			p = car(sc->args);
		}
		res = p->_object._port->kind & port_string;
		s_retbool(res);
	}

	case OP_SET_INPORT: /* set-input-port */
		sc->inport = car(sc->args);
		s_return(sc, sc->value);

	case OP_SET_OUTPORT: /* set-output-port */
		sc->outport = car(sc->args);
		s_return(sc, sc->value);

	case OP_RDSEXPR:
		switch (sc->tok) {
		case TOK_EOF:
			s_return(sc, sc->EOF_OBJ);
			/* NOTREACHED */
			/*
                * Commented out because we now skip comments in the scanner
                *
                         case TOK_COMMENT: {
                              int c;
                              while ((c=inchar(sc)) != '\n' && c!=EOF)
                                   ;
                              sc->tok = token(sc);
                              s_goto(sc,OP_RDSEXPR);
                         }
               */
		case TOK_VEC:
			s_save(sc, OP_RDVEC, sc->NIL, sc->NIL);
			/* fall through */
		case TOK_LPAREN:
			sc->tok = token(sc);
			if (sc->tok == TOK_RPAREN) {
				s_return(sc, sc->NIL);
			} else if (sc->tok == TOK_DOT) {
				Error_0(sc,
					"syntax error: illegal dot expression");
			} else {
				sc->nesting_stack[sc->file_i]++;
				s_save(sc, OP_RDLIST, sc->NIL, sc->NIL);
				s_goto(sc, OP_RDSEXPR);
			}
		case TOK_QUOTE:
			s_save(sc, OP_RDQUOTE, sc->NIL, sc->NIL);
			sc->tok = token(sc);
			s_goto(sc, OP_RDSEXPR);
		case TOK_BQUOTE:
			sc->tok = token(sc);
			if (sc->tok == TOK_VEC) {
				s_save(sc, OP_RDQQUOTEVEC, sc->NIL, sc->NIL);
				sc->tok = TOK_LPAREN;
				s_goto(sc, OP_RDSEXPR);
			} else {
				s_save(sc, OP_RDQQUOTE, sc->NIL, sc->NIL);
			}
			s_goto(sc, OP_RDSEXPR);
		case TOK_COMMA:
			s_save(sc, OP_RDUNQUOTE, sc->NIL, sc->NIL);
			sc->tok = token(sc);
			s_goto(sc, OP_RDSEXPR);
		case TOK_ATMARK:
			s_save(sc, OP_RDUQTSP, sc->NIL, sc->NIL);
			sc->tok = token(sc);
			s_goto(sc, OP_RDSEXPR);
		case TOK_ATOM:
			s_return(sc, mk_atom(sc, readstr_upto(sc, DELIMITERS)));
		case TOK_DQUOTE:
			x = readstrexp(sc);
			if (x == sc->F) {
				Error_0(sc, "Error reading string");
			}
			setimmutable(x);
			s_return(sc, x);
		case TOK_SHARP: {
			pointer f = find_slot_in_env(sc, sc->envir,
						     sc->SHARP_HOOK, 1);
			if (f == sc->NIL) {
				Error_0(sc, "undefined sharp expression");
			} else {
				sc->code =
					cons(sc, slot_value_in_env(f), sc->NIL);
				s_goto(sc, OP_EVAL);
			}
		}
		case TOK_SHARP_CONST:
			if ((x = mk_sharp_const(
				     sc, readstr_upto(sc, DELIMITERS))) ==
			    sc->NIL) {
				Error_0(sc, "undefined sharp expression");
			} else {
				s_return(sc, x);
			}
		default:
			Error_0(sc, "syntax error: illegal token");
		}
		break;

	case OP_RDLIST: {
		sc->args = cons(sc, sc->value, sc->args);
		sc->tok = token(sc);
		/* We now skip comments in the scanner
                    while (sc->tok == TOK_COMMENT) {
                         int c;
                         while ((c=inchar(sc)) != '\n' && c!=EOF)
                              ;
                         sc->tok = token(sc);
                    }
          */
		if (sc->tok == TOK_EOF) {
			s_return(sc, sc->EOF_OBJ);
		} else if (sc->tok == TOK_RPAREN) {
			int c = inchar(sc);
			if (c != '\n')
				backchar(sc, c);
#if SHOW_ERROR_LINE
			else if (sc->load_stack[sc->file_i].kind & port_file)
				sc->load_stack[sc->file_i].rep.stdio.curr_line++;
#endif
			sc->nesting_stack[sc->file_i]--;
			s_return(sc, reverse_in_place(sc, sc->NIL, sc->args));
		} else if (sc->tok == TOK_DOT) {
			s_save(sc, OP_RDDOT, sc->args, sc->NIL);
			sc->tok = token(sc);
			s_goto(sc, OP_RDSEXPR);
		} else {
			s_save(sc, OP_RDLIST, sc->args, sc->NIL);
			;
			s_goto(sc, OP_RDSEXPR);
		}
	}

	case OP_RDDOT:
		if (token(sc) != TOK_RPAREN) {
			Error_0(sc, "syntax error: illegal dot expression");
		} else {
			sc->nesting_stack[sc->file_i]--;
			s_return(sc, reverse_in_place(sc, sc->value, sc->args));
		}

	case OP_RDQUOTE:
		s_return(sc, cons(sc, sc->QUOTE, cons(sc, sc->value, sc->NIL)));

	case OP_RDQQUOTE:
		s_return(sc,
			 cons(sc, sc->QQUOTE, cons(sc, sc->value, sc->NIL)));

	case OP_RDQQUOTEVEC:
		s_return(sc, cons(sc, mk_symbol(sc, "apply"),
				  cons(sc, mk_symbol(sc, "vector"),
				       cons(sc,
					    cons(sc, sc->QQUOTE,
						 cons(sc, sc->value, sc->NIL)),
					    sc->NIL))));

	case OP_RDUNQUOTE:
		s_return(sc,
			 cons(sc, sc->UNQUOTE, cons(sc, sc->value, sc->NIL)));

	case OP_RDUQTSP:
		s_return(sc,
			 cons(sc, sc->UNQUOTESP, cons(sc, sc->value, sc->NIL)));

	case OP_RDVEC:
		/*sc->code=cons(sc,mk_proc(sc,OP_VECTOR),sc->value);
          s_goto(sc,OP_EVAL); Cannot be quoted*/
		/*x=cons(sc,mk_proc(sc,OP_VECTOR),sc->value);
          s_return(sc,x); Cannot be part of pairs*/
		/*sc->code=mk_proc(sc,OP_VECTOR);
          sc->args=sc->value;
          s_goto(sc,OP_APPLY);*/
		sc->args = sc->value;
		s_goto(sc, OP_VECTOR);

	/* ========== printing part ========== */
	case OP_P0LIST:
		if (is_vector(sc->args)) {
			putstr(sc, "#(");
			sc->args = cons(sc, sc->args, mk_integer(sc, 0));
			s_goto(sc, OP_PVECFROM);
		} else if (is_environment(sc->args)) {
			putstr(sc, "#<ENVIRONMENT>");
			s_return(sc, sc->T);
		} else if (!is_pair(sc->args)) {
			printatom(sc, sc->args, sc->print_flag);
			s_return(sc, sc->T);
		} else if (car(sc->args) == sc->QUOTE &&
			   ok_abbrev(cdr(sc->args))) {
			putstr(sc, "'");
			sc->args = cadr(sc->args);
			s_goto(sc, OP_P0LIST);
		} else if (car(sc->args) == sc->QQUOTE &&
			   ok_abbrev(cdr(sc->args))) {
			putstr(sc, "`");
			sc->args = cadr(sc->args);
			s_goto(sc, OP_P0LIST);
		} else if (car(sc->args) == sc->UNQUOTE &&
			   ok_abbrev(cdr(sc->args))) {
			putstr(sc, ",");
			sc->args = cadr(sc->args);
			s_goto(sc, OP_P0LIST);
		} else if (car(sc->args) == sc->UNQUOTESP &&
			   ok_abbrev(cdr(sc->args))) {
			putstr(sc, ",@");
			sc->args = cadr(sc->args);
			s_goto(sc, OP_P0LIST);
		} else {
			putstr(sc, "(");
			s_save(sc, OP_P1LIST, cdr(sc->args), sc->NIL);
			sc->args = car(sc->args);
			s_goto(sc, OP_P0LIST);
		}

	case OP_P1LIST:
		if (is_pair(sc->args)) {
			s_save(sc, OP_P1LIST, cdr(sc->args), sc->NIL);
			putstr(sc, " ");
			sc->args = car(sc->args);
			s_goto(sc, OP_P0LIST);
		} else if (is_vector(sc->args)) {
			s_save(sc, OP_P1LIST, sc->NIL, sc->NIL);
			putstr(sc, " . ");
			s_goto(sc, OP_P0LIST);
		} else {
			if (sc->args != sc->NIL) {
				putstr(sc, " . ");
				printatom(sc, sc->args, sc->print_flag);
			}
			putstr(sc, ")");
			s_return(sc, sc->T);
		}
	case OP_PVECFROM: {
		int i = ivalue_unchecked(cdr(sc->args));
		pointer vec = car(sc->args);
		int len = ivalue_unchecked(vec);
		if (i == len) {
			putstr(sc, ")");
			s_return(sc, sc->T);
		} else {
			pointer elem = vector_elem(vec, i);
			ivalue_unchecked(cdr(sc->args)) = i + 1;
			s_save(sc, OP_PVECFROM, sc->args, sc->NIL);
			sc->args = elem;
			if (i > 0)
				putstr(sc, " ");
			s_goto(sc, OP_P0LIST);
		}
	}

	default:
		snprintf(sc->strbuff, STRBUFFSIZE, "%d: illegal operator",
			 sc->op);
		Error_0(sc, sc->strbuff);
	}
	return sc->T;
}

static pointer opexe_6(scheme *sc, enum scheme_opcodes op)
{
	pointer x, y;
	long v;

	switch (op) {
	case OP_LIST_LENGTH: /* length */ /* a.k */
		v = list_length(sc, car(sc->args));
		if (v < 0) {
			Error_1(sc, "length: not a list:", car(sc->args));
		}
		s_return(sc, mk_integer(sc, v));

	case OP_ASSQ: /* assq */ /* a.k */
		x = car(sc->args);
		for (y = cadr(sc->args); is_pair(y); y = cdr(y)) {
			if (!is_pair(car(y))) {
				Error_0(sc,
					"unable to handle non pair element");
			}
			if (x == caar(y))
				break;
		}
		if (is_pair(y)) {
			s_return(sc, car(y));
		} else {
			s_return(sc, sc->F);
		}

	case OP_GET_CLOSURE: /* get-closure-code */ /* a.k */
		sc->args = car(sc->args);
		if (sc->args == sc->NIL) {
			s_return(sc, sc->F);
		} else if (is_closure(sc->args)) {
			s_return(sc,
				 cons(sc, sc->LAMBDA, closure_code(sc->value)));
		} else if (is_macro(sc->args)) {
			s_return(sc,
				 cons(sc, sc->LAMBDA, closure_code(sc->value)));
		} else {
			s_return(sc, sc->F);
		}
	case OP_CLOSUREP: /* closure? */
		/*
           * Note, macro object is also a closure.
           * Therefore, (closure? <#MACRO>) ==> #t
           */
		s_retbool(is_closure(car(sc->args)));
	case OP_MACROP: /* macro? */
		s_retbool(is_macro(car(sc->args)));
	default:
		snprintf(sc->strbuff, STRBUFFSIZE, "%d: illegal operator",
			 sc->op);
		Error_0(sc, sc->strbuff);
	}
	return sc->T; /* NOTREACHED */
}

typedef pointer (*dispatch_func)(scheme *, enum scheme_opcodes);

typedef int (*test_predicate)(pointer);
static int is_any(pointer p)
{
	return 1;
}

static int is_nonneg(pointer p)
{
	return ivalue(p) >= 0 && is_integer(p);
}

/* Correspond carefully with following defines! */
static struct {
	test_predicate fct;
	const char *kind;
} tests[] = { { 0, 0 }, /* unused */
	      { is_any, 0 },
	      { is_string, "string" },
	      { is_symbol, "symbol" },
	      { is_port, "port" },
	      { is_inport, "input port" },
	      { is_outport, "output port" },
	      { is_environment, "environment" },
	      { is_pair, "pair" },
	      { 0, "pair or '()" },
	      { is_character, "character" },
	      { is_vector, "vector" },
	      { is_number, "number" },
	      { is_integer, "integer" },
	      { is_nonneg, "non-negative integer" } };

#define TST_NONE 0
#define TST_ANY "\001"
#define TST_STRING "\002"
#define TST_SYMBOL "\003"
#define TST_PORT "\004"
#define TST_INPORT "\005"
#define TST_OUTPORT "\006"
#define TST_ENVIRONMENT "\007"
#define TST_PAIR "\010"
#define TST_LIST "\011"
#define TST_CHAR "\012"
#define TST_VECTOR "\013"
#define TST_NUMBER "\014"
#define TST_INTEGER "\015"
#define TST_NATURAL "\016"

typedef struct {
	dispatch_func func;
	char *name;
	int min_arity;
	int max_arity;
	char *arg_tests_encoding;
} op_code_info;

#define INF_ARG 0xffff

static op_code_info dispatch_table[] = {
#define _OP_DEF(A, B, C, D, E, OP) { A, B, C, D, E },
#include "opdefines.h"
	{ 0 }
};

static const char *procname(pointer x)
{
	int n = procnum(x);
	const char *name = dispatch_table[n].name;
	if (name == 0) {
		name = "ILLEGAL!";
	}
	return name;
}

/* kernel of this interpreter */
static void Eval_Cycle(scheme *sc, enum scheme_opcodes op)
{
	sc->op = op;
	for (;;) {
		op_code_info *pcd = dispatch_table + sc->op;
		if (pcd->name !=
		    0) { /* if built-in function, check arguments */
			char msg[STRBUFFSIZE];
			int ok = 1;
			int n = list_length(sc, sc->args);

			/* Check number of arguments */
			if (n < pcd->min_arity) {
				ok = 0;
				snprintf(msg, STRBUFFSIZE,
					 "%s: needs%s %d argument(s)",
					 pcd->name,
					 pcd->min_arity == pcd->max_arity ?
						 "" :
						       " at least",
					 pcd->min_arity);
			}
			if (ok && n > pcd->max_arity) {
				ok = 0;
				snprintf(msg, STRBUFFSIZE,
					 "%s: needs%s %d argument(s)",
					 pcd->name,
					 pcd->min_arity == pcd->max_arity ?
						 "" :
						       " at most",
					 pcd->max_arity);
			}
			if (ok) {
				if (pcd->arg_tests_encoding != 0) {
					int i = 0;
					int j;
					const char *t = pcd->arg_tests_encoding;
					pointer arglist = sc->args;
					do {
						pointer arg = car(arglist);
						j = (int)t[0];
						if (j == TST_LIST[0]) {
							if (arg != sc->NIL &&
							    !is_pair(arg))
								break;
						} else {
							if (!tests[j].fct(arg))
								break;
						}

						if (t[1] !=
						    0) { /* last test is replicated as necessary */
							t++;
						}
						arglist = cdr(arglist);
						i++;
					} while (i < n);
					if (i < n) {
						ok = 0;
						snprintf(
							msg, STRBUFFSIZE,
							"%s: argument %d must be: %s",
							pcd->name, i + 1,
							tests[j].kind);
					}
				}
			}
			if (!ok) {
				if (_Error_1(sc, msg, 0) == sc->NIL) {
					return;
				}
				pcd = dispatch_table + sc->op;
			}
		}
		ok_to_freely_gc(sc);
		if (pcd->func(sc, (enum scheme_opcodes)sc->op) == sc->NIL) {
			return;
		}
		if (sc->no_memory) {
			fprintf(stderr, "No memory!\n");
			return;
		}
	}
}

/* ========== Initialization of internal keywords ========== */

static void assign_syntax(scheme *sc, char *name)
{
	pointer x;
	x = oblist_add_by_name(sc, name);
	typeflag(x) |= T_SYNTAX;
}

static void assign_proc(scheme *sc, enum scheme_opcodes op, char *name)
{
	pointer x, y;
	x = mk_symbol(sc, name);
	y = mk_proc(sc, op);
	new_slot_in_env(sc, x, y);
}

static pointer mk_proc(scheme *sc, enum scheme_opcodes op)
{
	pointer y;
	y = get_cell(sc, sc->NIL, sc->NIL);
	typeflag(y) = (T_PROC | T_ATOM);
	ivalue_unchecked(y) = (long)op;
	set_num_integer(y);
	return y;
}

/* Hard-coded for the given keywords. Remember to rewrite if more are added! */
static int syntaxnum(pointer p)
{
	const char *s = strvalue(car(p));
	switch (strlength(car(p))) {
	case 2:
		if (s[0] == 'i')
			return OP_IF0; /* if */
		else
			return OP_OR0; /* or */
	case 3:
		if (s[0] == 'a')
			return OP_AND0; /* and */
		else
			return OP_LET0; /* let */
	case 4:
		switch (s[3]) {
		case 'e':
			return OP_CASE0; /* case */
		case 'd':
			return OP_COND0; /* cond */
		case '*':
			return OP_LET0AST; /* let* */
		default:
			return OP_SET0; /* set! */
		}
	case 5:
		switch (s[2]) {
		case 'g':
			return OP_BEGIN; /* begin */
		case 'l':
			return OP_DELAY; /* delay */
		case 'c':
			return OP_MACRO0; /* macro */
		default:
			return OP_QUOTE; /* quote */
		}
	case 6:
		switch (s[2]) {
		case 'm':
			return OP_LAMBDA; /* lambda */
		case 'f':
			return OP_DEF0; /* define */
		default:
			return OP_LET0REC; /* letrec */
		}
	default:
		return OP_C0STREAM; /* cons-stream */
	}
}

/* initialization of TinyScheme */

scheme *scheme_init_new()
{
	scheme *sc = (scheme *)malloc(sizeof(scheme));
	if (!scheme_init(sc)) {
		free(sc);
		return 0;
	} else {
		return sc;
	}
}

scheme *scheme_init_new_custom_alloc(func_alloc malloc, func_dealloc free)
{
	scheme *sc = (scheme *)malloc(sizeof(scheme));
	if (!scheme_init_custom_alloc(sc, malloc, free)) {
		free(sc);
		return 0;
	} else {
		return sc;
	}
}

int scheme_init(scheme *sc)
{
	return scheme_init_custom_alloc(sc, malloc, free);
}

int scheme_init_custom_alloc(scheme *sc, func_alloc malloc, func_dealloc free)
{
	int i, n = sizeof(dispatch_table) / sizeof(dispatch_table[0]);
	pointer x;

	num_zero.is_fixnum = 1;
	num_zero.value.ivalue = 0;
	num_one.is_fixnum = 1;
	num_one.value.ivalue = 1;

	sc->gensym_cnt = 0;
	sc->malloc = malloc;
	sc->free = free;
	sc->last_cell_seg = -1;
	sc->sink = &sc->_sink;
	sc->NIL = &sc->_NIL;
	sc->T = &sc->_HASHT;
	sc->F = &sc->_HASHF;
	sc->EOF_OBJ = &sc->_EOF_OBJ;
	sc->free_cell = &sc->_NIL;
	sc->fcells = 0;
	sc->no_memory = 0;
	sc->inport = sc->NIL;
	sc->outport = sc->NIL;
	sc->save_inport = sc->NIL;
	sc->loadport = sc->NIL;
	sc->nesting = 0;

	if (alloc_cellseg(sc, FIRST_CELLSEGS) != FIRST_CELLSEGS) {
		sc->no_memory = 1;
		return 0;
	}
	sc->gc_verbose = 0;
	dump_stack_initialize(sc);
	sc->code = sc->NIL;
	sc->tracing = 0;

	/* init sc->NIL */
	typeflag(sc->NIL) = (T_ATOM | MARK);
	car(sc->NIL) = cdr(sc->NIL) = sc->NIL;
	/* init T */
	typeflag(sc->T) = (T_ATOM | MARK);
	car(sc->T) = cdr(sc->T) = sc->T;
	/* init F */
	typeflag(sc->F) = (T_ATOM | MARK);
	car(sc->F) = cdr(sc->F) = sc->F;
	/* init sink */
	typeflag(sc->sink) = (T_PAIR | MARK);
	car(sc->sink) = sc->NIL;
	/* init c_nest */
	sc->c_nest = sc->NIL;

	sc->oblist = oblist_initial_value(sc);
	/* init global_env */
	new_frame_in_env(sc, sc->NIL);
	sc->global_env = sc->envir;
	/* init else */
	x = mk_symbol(sc, "else");
	new_slot_in_env(sc, x, sc->T);

	assign_syntax(sc, "lambda");
	assign_syntax(sc, "quote");
	assign_syntax(sc, "define");
	assign_syntax(sc, "if");
	assign_syntax(sc, "begin");
	assign_syntax(sc, "set!");
	assign_syntax(sc, "let");
	assign_syntax(sc, "let*");
	assign_syntax(sc, "letrec");
	assign_syntax(sc, "cond");
	assign_syntax(sc, "delay");
	assign_syntax(sc, "and");
	assign_syntax(sc, "or");
	assign_syntax(sc, "cons-stream");
	assign_syntax(sc, "macro");
	assign_syntax(sc, "case");

	for (i = 0; i < n; i++) {
		if (dispatch_table[i].name != 0) {
			assign_proc(sc, (enum scheme_opcodes)i,
				    dispatch_table[i].name);
		}
	}

	/* initialization of global pointers to special symbols */
	sc->LAMBDA = mk_symbol(sc, "lambda");
	sc->QUOTE = mk_symbol(sc, "quote");
	sc->QQUOTE = mk_symbol(sc, "quasiquote");
	sc->UNQUOTE = mk_symbol(sc, "unquote");
	sc->UNQUOTESP = mk_symbol(sc, "unquote-splicing");
	sc->FEED_TO = mk_symbol(sc, "=>");
	sc->COLON_HOOK = mk_symbol(sc, "*colon-hook*");
	sc->ERROR_HOOK = mk_symbol(sc, "*error-hook*");
	sc->SHARP_HOOK = mk_symbol(sc, "*sharp-hook*");
	sc->COMPILE_HOOK = mk_symbol(sc, "*compile-hook*");

	return !sc->no_memory;
}

void scheme_set_input_port_file(scheme *sc, FILE *fin)
{
	sc->inport = port_from_file(sc, fin, port_input);
}

void scheme_set_input_port_string(scheme *sc, char *start, char *past_the_end)
{
	sc->inport = port_from_string(sc, start, past_the_end, port_input);
}

void scheme_set_output_port_file(scheme *sc, FILE *fout)
{
	sc->outport = port_from_file(sc, fout, port_output);
}

void scheme_set_output_port_string(scheme *sc, char *start, char *past_the_end)
{
	sc->outport = port_from_string(sc, start, past_the_end, port_output);
}

void scheme_set_external_data(scheme *sc, void *p)
{
	sc->ext_data = p;
}

void scheme_deinit(scheme *sc)
{
	int i;

#if SHOW_ERROR_LINE
	char *fname;
#endif

	sc->oblist = sc->NIL;
	sc->global_env = sc->NIL;
	dump_stack_free(sc);
	sc->envir = sc->NIL;
	sc->code = sc->NIL;
	sc->args = sc->NIL;
	sc->value = sc->NIL;
	if (is_port(sc->inport)) {
		typeflag(sc->inport) = T_ATOM;
	}
	sc->inport = sc->NIL;
	sc->outport = sc->NIL;
	if (is_port(sc->save_inport)) {
		typeflag(sc->save_inport) = T_ATOM;
	}
	sc->save_inport = sc->NIL;
	if (is_port(sc->loadport)) {
		typeflag(sc->loadport) = T_ATOM;
	}
	sc->loadport = sc->NIL;
	sc->gc_verbose = 0;
	gc(sc, sc->NIL, sc->NIL);

	for (i = 0; i <= sc->last_cell_seg; i++) {
		sc->free(sc->alloc_seg[i]);
	}

#if SHOW_ERROR_LINE
	for (i = 0; i <= sc->file_i; i++) {
		if (sc->load_stack[i].kind & port_file) {
			fname = sc->load_stack[i].rep.stdio.filename;
			if (fname)
				sc->free(fname);
		}
	}
#endif
}

void scheme_load_file(scheme *sc, FILE *fin)
{
	scheme_load_named_file(sc, fin, 0);
}

void scheme_load_named_file(scheme *sc, FILE *fin, const char *filename)
{
	dump_stack_reset(sc);
	sc->envir = sc->global_env;
	sc->file_i = 0;
	sc->load_stack[0].kind = port_input | port_file;
	sc->load_stack[0].rep.stdio.file = fin;
	sc->loadport = mk_port(sc, sc->load_stack);
	sc->retcode = 0;

#if SHOW_ERROR_LINE
	sc->load_stack[0].rep.stdio.curr_line = 0;
	if (fin != stdin && filename)
		sc->load_stack[0].rep.stdio.filename =
			store_string(sc, strlen(filename), filename, 0);
	else
		sc->load_stack[0].rep.stdio.filename = NULL;
#endif

	sc->inport = sc->loadport;
	sc->args = mk_integer(sc, sc->file_i);
	Eval_Cycle(sc, OP_T0LVL);
	typeflag(sc->loadport) = T_ATOM;
	if (sc->retcode == 0) {
		sc->retcode = sc->nesting != 0;
	}
}

void scheme_load_string(scheme *sc, const char *cmd)
{
	dump_stack_reset(sc);
	sc->envir = sc->global_env;
	sc->file_i = 0;
	sc->load_stack[0].kind = port_input | port_string;
	sc->load_stack[0].rep.string.start =
		(char *)cmd; /* This func respects const */
	sc->load_stack[0].rep.string.past_the_end = (char *)cmd + strlen(cmd);
	sc->load_stack[0].rep.string.curr = (char *)cmd;
	sc->loadport = mk_port(sc, sc->load_stack);
	sc->retcode = 0;
	sc->inport = sc->loadport;
	sc->args = mk_integer(sc, sc->file_i);
	Eval_Cycle(sc, OP_T0LVL);
	typeflag(sc->loadport) = T_ATOM;
	if (sc->retcode == 0) {
		sc->retcode = sc->nesting != 0;
	}
}

void scheme_define(scheme *sc, pointer envir, pointer symbol, pointer value)
{
	pointer x;

	x = find_slot_in_env(sc, envir, symbol, 0);
	if (x != sc->NIL) {
		set_slot_in_env(sc, x, value);
	} else {
		new_slot_spec_in_env(sc, envir, symbol, value);
	}
}

void scheme_register_foreign_func(scheme *sc, scheme_registerable *sr)
{
	scheme_define(sc, sc->global_env, mk_symbol(sc, sr->name),
		      mk_foreign_func(sc, sr->f));
}

void scheme_register_foreign_func_list(scheme *sc, scheme_registerable *list,
				       int count)
{
	int i;
	for (i = 0; i < count; i++) {
		scheme_register_foreign_func(sc, list + i);
	}
}

pointer scheme_apply0(scheme *sc, const char *procname)
{
	return scheme_eval(sc, cons(sc, mk_symbol(sc, procname), sc->NIL));
}

void save_from_C_call(scheme *sc)
{
	pointer saved_data =
		cons(sc, car(sc->sink), cons(sc, sc->envir, sc->dump));
	/* Push */
	sc->c_nest = cons(sc, saved_data, sc->c_nest);
	/* Truncate the dump stack so TS will return here when done, not
        directly resume pre-C-call operations. */
	dump_stack_reset(sc);
}
void restore_from_C_call(scheme *sc)
{
	car(sc->sink) = caar(sc->c_nest);
	sc->envir = cadar(sc->c_nest);
	sc->dump = cdr(cdar(sc->c_nest));
	/* Pop */
	sc->c_nest = cdr(sc->c_nest);
}

/* "func" and "args" are assumed to be already eval'ed. */
pointer scheme_call(scheme *sc, pointer func, pointer args)
{
	save_from_C_call(sc);
	sc->envir = sc->global_env;
	sc->args = args;
	sc->code = func;
	sc->retcode = 0;
	Eval_Cycle(sc, OP_APPLY);
	restore_from_C_call(sc);
	return sc->value;
}

pointer scheme_eval(scheme *sc, pointer obj)
{
	save_from_C_call(sc);
	sc->args = sc->NIL;
	sc->code = obj;
	sc->retcode = 0;
	Eval_Cycle(sc, OP_EVAL);
	restore_from_C_call(sc);
	return sc->value;
}

/*
Local variables:
c-file-style: "k&r"
End:
*/