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Add StateT Monad Transformer #952

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Add StateT Monad Transformer #952

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de0cc6b
Add StateT Monad Transformer
JasonGross Apr 20, 2023
b33c544
Add {get,set,update}_state
JasonGross Apr 20, 2023
d538d2f
Adjust state monad utils
JasonGross Apr 20, 2023
d0d517b
Unset Universe Minimization ToSet in monad_utils
JasonGross Apr 20, 2023
54f23e1
Add State.run_drop_state
JasonGross Apr 24, 2023
bb7f52f
Rename run_drop_state to evalStateT to match with ExtLib
JasonGross Apr 24, 2023
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23 changes: 23 additions & 0 deletions utils/theories/monad_utils.v
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ Import ListNotations.

Set Universe Polymorphism.
Set Polymorphic Inductive Cumulativity.
Unset Universe Minimization ToSet.

Class Monad@{d c} (m : Type@{d} -> Type@{c}) : Type :=
{ ret : forall {t : Type@{d}}, t -> m t
Expand Down Expand Up @@ -69,6 +70,28 @@ Import MCMonadNotation.

Open Scope monad.

(* state is underneath the other monad *)
Definition StateT S M T := S -> M (T * S)%type.
Definition StateT_Monad {S T} {TM : Monad T} : Monad (StateT S T) :=
{| ret A a st := ret (a, st) ;
bind A B m f st := '(m, st) <- m st;; f m st
|}.
#[export] Hint Extern 1 (Monad (StateT ?S ?T)) => simple apply (@StateT_Monad S T) : typeclass_instances.

Module State.
Definition get {S T} {TM : Monad T} : StateT S T S
:= fun s => ret (s, s).
Definition update {S T} {TM : Monad T} (f : S -> S) : StateT S T unit
:= fun s => ret (tt, f s).
Definition set {S T} {TM : Monad T} (s : S) : StateT S T unit
:= update (fun _ => s).
Definition lift {S T} {TM : Monad T} {A} (m : T A) : StateT S T A
:= fun s => v <- m;; ret (v, s).
Definition evalStateT {S T A} {TM : Monad T} (p : StateT S T A) (st : S) : T A
:= '(v, st) <- p st;;
ret v.
End State.

Section MapOpt.
Context {A} {B} (f : A -> option B).

Expand Down