Commit 8c50463e by POTTIER Francois

New OCaml exercise.

parent b88b92d3
(* -------------------------------------------------------------------------- *)
(* The type of lambda-terms, in de Bruijn's representation. *)
type var = int (* a de Bruijn index *)
type term =
| Var of var
| Lam of (* bind: *) term
| App of term * term
| Let of (* bind: *) term * term
(* -------------------------------------------------------------------------- *)
(* An environment-based big-step interpreter. This is the same interpreter
that we programmed in Coq, except here, in OCaml, fuel is not needed. *)
type cvalue =
| Clo of (* bind: *) term * cenv
and cenv =
cvalue list
let empty : cenv =
[]
exception RuntimeError
let lookup (e : cenv) (x : var) : cvalue =
try
List.nth e x
with Failure _ ->
raise RuntimeError
let rec eval (e : cenv) (t : term) : cvalue =
match t with
| Var x ->
lookup e x
| Lam t ->
Clo (t, e)
| App (t1, t2) ->
let cv1 = eval e t1 in
let cv2 = eval e t2 in
let Clo (u1, e') = cv1 in
eval (cv2 :: e') u1
| Let (t1, t2) ->
eval (eval e t1 :: e) t2
(* -------------------------------------------------------------------------- *)
(* The CPS-transformed interpreter. *)
let rec evalk (e : cenv) (t : term) (k : cvalue -> 'a) : 'a =
assert false
let eval (e : cenv) (t : term) : cvalue =
evalk e t (fun cv -> cv)
(* -------------------------------------------------------------------------- *)
(* The CPS-transformed, defunctionalized interpreter. *)
type kont
let rec evalkd (e : cenv) (t : term) (k : kont) : cvalue =
assert false
and apply (k : kont) (cv : cvalue) : cvalue =
assert false
let eval e t =
evalkd e t (assert false)
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