Require Export Computation.Monad.
Require Export Computation.Termination.
(* evaluate up to [n] computation steps *)
Fixpoint bounded_eval (A:Set) (n:nat) (c:#A) {struct n} : option A :=
match n with
| O => None
| (S n') =>
match c with
| Return b => Some b
| Bind _ f c' =>
match (bounded_eval _ n' c') with
| None => None
| Some a => bounded_eval A n' (f a)
end
end
end.
Inductive Unit : Set := unit : Unit.
(*
* In theory we'd like to be able to do this (below), but it violates
* the Prop/Set separation:
*
* "Elimination of an inductive object of sort Prop is not allowed on a
* predicate in sort Set because proofs can be eliminated only to
* build proofs."
*)
(*
Definition eval (A:Set) (c:#A) (t:Terminates c) : A :=
match t with
| (Terminates_intro t') =>
match t' with
| (ex_intro x y) => x
end
end.
*)
Definition eval (A:Set) (c:#A) (t:Terminates c) : A :=
match eval' c Unit (Return unit) (termination_is_safe A c t) with
| exist x pf => x
end.
Implicit Arguments eval [A].
Implicit Arguments bounded_eval [A].