[asr->python] add string visitors

[khushi-411]

• add tests

[Thirumalai-Shaktivel]

Yes, please add tests

[Thirumalai-Shaktivel]

Suggested change

	if (x.m_start) {
	r += "[";
	visit_expr(*x.m_start);
	r += s;
	}
	if (x.m_end) {
	r += ":";
	visit_expr(*x.m_end);
	r += s;
	}
	if (x.m_step) {
	r += ":";
	visit_expr(*x.m_step);
	r += s;
	r += "]";
	} else {
	r += "]";
	}
	r += "[";
	if (x.m_start) {
	visit_expr(*x.m_start);
	r += s;
	}
	r += ":";
	if (x.m_end) {
	visit_expr(*x.m_end);
	r += s;
	}
	if (x.m_step) {
	r += ":";
	visit_expr(*x.m_step);
	r += s;
	}
	r += "]";

I suggested this changes because of the following cases:

s: str = "12345"
print(s[:])
print(s[3:])
print(s[3:4:])

[Thirumalai-Shaktivel]

Does LPython represents StringFormat in the ASR? (If we don't support, let's implement this later? )
I think we don't properly support f-strings yet.

[khushi-411]

Yes, I added these because there is an entry for StringFormat. Here:

lpython/src/libasr/ASR.asdl

Line 305 in 7aa7084

| StringFormat(expr fmt, expr* args, string_format_kind kind, ttype type, expr? value)

Do you think we should keep it? Thanks

[Thirumalai-Shaktivel]

Yes, we have an entry in ASR.asdl, but LPython doesn't utilise it yet.
So, I think let's remove it for now. And handle it correctly once LPython supports f-strings.