From fdf7145a92a4be1e9780372b8de5c4770ee06d33 Mon Sep 17 00:00:00 2001
From: Peter <peterhsaxton@gmail.com>
Date: Fri, 14 Aug 2020 08:50:36 +0100
Subject: test and implement unzip

---
 src/gleam/list.gleam       | 11 +++++++++++
 test/gleam/list_test.gleam |  8 ++++++++
 2 files changed, 19 insertions(+)

diff --git a/src/gleam/list.gleam b/src/gleam/list.gleam
index 06e5a33..c82db2e 100644
--- a/src/gleam/list.gleam
+++ b/src/gleam/list.gleam
@@ -623,6 +623,17 @@ pub fn strict_zip(
   }
 }
 
+fn do_unzip(input, xs, ys) {
+  case input {
+    [] -> tuple(reverse(xs), reverse(ys))
+    [tuple(x, y), ..rest] -> do_unzip(rest, [x, ..xs], [y, ..ys])
+  }
+}
+
+pub fn unzip(input: List(tuple(a, b))) -> tuple(List(a), List(b)) {
+  do_unzip(input, [], [])
+}
+
 /// Insert a given value between each existing element in a given list.
 ///
 /// This function runs in linear time and copies the list.
diff --git a/test/gleam/list_test.gleam b/test/gleam/list_test.gleam
index 31f8f27..eff9fac 100644
--- a/test/gleam/list_test.gleam
+++ b/test/gleam/list_test.gleam
@@ -264,6 +264,14 @@ pub fn strict_zip_test() {
   |> should.equal(Error(list.LengthMismatch))
 }
 
+pub fn unzip_test() {
+  list.unzip([tuple(1, 2), tuple(3, 4)])
+  |> should.equal(tuple([1, 3], [2, 4]))
+
+  list.unzip([])
+  |> should.equal(tuple([], []))
+}
+
 pub fn intersperse_test() {
   list.intersperse([1, 2, 3], 4)
   |> should.equal([1, 4, 2, 4, 3])
-- 
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