ocaml: phase 5.1 lambda_calc.ml baseline (17/17 pass)

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.

lib/ocaml/baseline/expected.json

@@ -7,6 +7,7 @@
   "factorial.ml": 3628800,
   "fizzbuzz.ml": 57,
   "list_ops.ml": 30,
+  "lambda_calc.ml": 7,
   "memo_fib.ml": 75025,
   "module_use.ml": 3,
   "mutable_record.ml": 10,

lib/ocaml/baseline/lambda_calc.ml

@@ -0,0 +1,41 @@
+(* Baseline: untyped lambda calculus with closures over a Hashtbl env *)
+type term =
+  | Var of string
+  | Abs of string * term
+  | App of term * term
+  | Num of int
+;;
+
+type value =
+  | VNum of int
+  | VClos of string * term * (string * value) list
+;;
+
+let rec lookup name env =
+  match env with
+  | [] -> failwith "unbound"
+  | (n, v) :: t -> if n = name then v else lookup name t
+;;
+
+let rec eval env t =
+  match t with
+  | Num n -> VNum n
+  | Var x -> lookup x env
+  | Abs (x, body) -> VClos (x, body, env)
+  | App (f, a) ->
+    let fv = eval env f in
+    let av = eval env a in
+    (match fv with
+     | VClos (param, body, captured) ->
+       eval ((param, av) :: captured) body
+     | _ -> failwith "not a function")
+;;
+
+let unwrap v = match v with VNum n -> n | _ -> failwith "not a number" ;;
+
+(* (\x. \y. x) 7 99 = 7 *)
+let term =
+  App (App (Abs ("x", Abs ("y", Var "x")), Num 7), Num 99)
+;;
+
+unwrap (eval [] term)