ocaml: phase 5.1 safe_div.ml baseline + Result.equal/compare/iter_error (+3 tests, 592 total)

safe_div.ml: integer division returning Result. Sum-safe folds pairs,
skipping the Error branches.

  [(10,2); (20,4); (30,0); (50,5)]   ->  5 + 5 + 0 + 10 = 20

Result module additions (mirroring real OCaml's signatures):

  equal eq_ok eq_err a b
  compare cmp_ok cmp_err a b      Ok < Error (i.e. Ok x compared to
                                  Error e returns -1)
  iter_error f r

  Result.equal (=) (=) (Ok 1) (Ok 1)              = true
  Result.compare compare compare (Ok 5) (Ok 3)    = 1
  Result.compare compare compare (Ok 1) (Error _) = -1

30 baseline programs total.

lib/ocaml/baseline/safe_div.ml

@@ -0,0 +1,14 @@
+let safe_div a b =
+  if b = 0 then Error "division by zero"
+  else Ok (a / b)
+
+let sum_safe pairs =
+  List.fold_left (fun acc (a, b) ->
+    match safe_div a b with
+    | Ok q -> acc + q
+    | Error _ -> acc
+  ) 0 pairs
+
+;;
+
+sum_safe [(10, 2); (20, 4); (30, 0); (50, 5)]