ocaml: phase 5.1 expr_eval.ml baseline (9/9 pass)

A tiny arithmetic-expression evaluator using:
  type expr = Lit of int | Add of expr*expr | Mul of expr*expr | Neg of expr
  let rec eval e = match e with | Lit n -> n | Add (a,b) -> ...

Exercises type-decl + multi-arg ctor + recursive match end-to-end.
Per-program timeout in run.sh bumped to 120s.

lib/ocaml/baseline/expr_eval.ml

@@ -0,0 +1,19 @@
+(* Baseline: a tiny expression evaluator using ADTs + match *)
+type expr =
+  | Lit of int
+  | Add of expr * expr
+  | Mul of expr * expr
+  | Neg of expr
+;;
+
+let rec eval e =
+  match e with
+  | Lit n -> n
+  | Add (a, b) -> eval a + eval b
+  | Mul (a, b) -> eval a * eval b
+  | Neg x -> 0 - eval x
+;;
+
+(* (1 + 2) * (3 + 4) - 5 = 21 - 5 = 16 *)
+eval
+  (Add (Mul (Add (Lit 1, Lit 2), Add (Lit 3, Lit 4)), Neg (Lit 5)))