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Untyped lambda calculus interpreter inside OCaml-on-SX: type term = Var | Abs of string * term | App | Num of int type value = VNum of int | VClos of string * term * env let rec eval env t = match t with ... (\x.\y.x) 7 99 = 7. The substrate handles two ADTs, recursive eval, closure-based env, and pattern matching all written as a single self-contained OCaml program — strong validation.
42 lines
926 B
OCaml
42 lines
926 B
OCaml
(* Baseline: untyped lambda calculus with closures over a Hashtbl env *)
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type term =
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| Var of string
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| Abs of string * term
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| App of term * term
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| Num of int
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;;
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type value =
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| VNum of int
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| VClos of string * term * (string * value) list
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;;
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let rec lookup name env =
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match env with
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| [] -> failwith "unbound"
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| (n, v) :: t -> if n = name then v else lookup name t
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;;
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let rec eval env t =
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match t with
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| Num n -> VNum n
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| Var x -> lookup x env
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| Abs (x, body) -> VClos (x, body, env)
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| App (f, a) ->
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let fv = eval env f in
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let av = eval env a in
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(match fv with
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| VClos (param, body, captured) ->
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eval ((param, av) :: captured) body
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| _ -> failwith "not a function")
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;;
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let unwrap v = match v with VNum n -> n | _ -> failwith "not a number" ;;
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(* (\x. \y. x) 7 99 = 7 *)
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let term =
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App (App (Abs ("x", Abs ("y", Var "x")), Num 7), Num 99)
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;;
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unwrap (eval [] term)
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