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From mininix Require Export res lambda.operational_props.
From stdpp Require Import options.
Module Import lambda.
Export lambda.
Inductive thunk :=
Thunk { thunk_env : gmap string thunk; thunk_expr : expr }.
Add Printing Constructor thunk.
Notation env := (gmap string thunk).
Inductive val :=
| VString (s : string)
| VClo (x : string) (E : env) (e : expr).
Global Instance maybe_VClo : Maybe3 VClo := λ v,
if v is VClo x E e then Some (x, E, e) else None.
Definition interp1 (interp : env → expr → res val) (E : env) (e : expr) : res val :=
match e with
| EString s =>
mret (VString s)
| EId x =>
t ← Res (E !! x);
interp (thunk_env t) (thunk_expr t)
| EAbs x e =>
mret (VClo x E e)
| EApp e1 e2 =>
v1 ← interp E e1;
'(x, E', e') ← Res (maybe3 VClo v1);
interp (<[x:=Thunk E e2]> E') e'
end.
Fixpoint interp (n : nat) (E : env) (e : expr) : res val :=
match n with
| O => NoFuel
| S n => interp1 (interp n) E e
end.
Global Opaque interp.
End lambda.
Add Printing Constructor lambda.thunk.
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