ocaml: phase 5.1 zip_unzip.ml baseline (zip/unzip round-trip, sum-product = 1000)

zip walks both lists in lockstep, truncating at the shorter. unzip
uses tuple-pattern destructuring on the recursive result.

  let pairs = zip [1;2;3;4] [10;20;30;40] in
  let (xs, ys) = unzip pairs in
  List.fold_left (+) 0 xs * List.fold_left (+) 0 ys
  = 10 * 100
  = 1000

Exercises:
  - tuple-cons patterns in match scrutinee: 'match (xs, ys) with'
  - tuple constructor in return value: '(a :: la, b :: lb)'
  - the iter-98 let-tuple destructuring: 'let (la, lb) = unzip rest'

53 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -48,6 +48,7 @@
   "safe_div.ml": 20,
   "shuffle.ml": 55,
   "word_freq.ml": 8,
+  "zip_unzip.ml": 1000,
   "sieve.ml": 15,
   "sum_squares.ml": 385,
   "unique_set.ml": 9,

lib/ocaml/baseline/zip_unzip.ml

@@ -0,0 +1,18 @@
+let rec zip xs ys =
+  match (xs, ys) with
+  | ([], _) -> []
+  | (_, []) -> []
+  | (x :: xs', y :: ys') -> (x, y) :: zip xs' ys'
+
+let rec unzip pairs =
+  match pairs with
+  | [] -> ([], [])
+  | (a, b) :: rest ->
+    let (la, lb) = unzip rest in
+    (a :: la, b :: lb)
+
+;;
+
+let pairs = zip [1;2;3;4] [10;20;30;40] in
+let (xs, ys) = unzip pairs in
+List.fold_left (+) 0 xs * List.fold_left (+) 0 ys