From 41562c9139b36536efd267c4220b0288ce4be26a Mon Sep 17 00:00:00 2001
From: Tobias Pflug <tobias.pflug@gmail.com>
Date: Mon, 23 May 2016 21:14:01 +0200
Subject: [PATCH] Add S.reverse

---
 index.js        | 22 ++++++++++++++++++++++
 test/reverse.js | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 test/reverse.js

diff --git a/index.js b/index.js
index cc4ed736..dc5b14c1 100644
--- a/index.js
+++ b/index.js
@@ -2441,6 +2441,28 @@
         return n < 0 || negativeZero(n) ? Nothing() : slice(0, -n, xs);
       });
 
+  //# reverse :: [a] -> [a]
+  //.
+  //. Returns the elements of the given list in reverse order.
+  //.
+  //. ```javascript
+  //. > S.reverse([1, 2, 3])
+  //. [3, 2, 1]
+  //.
+  //. > S.reverse('abc')
+  //. 'cba'
+  //. ```
+  S.reverse =
+  def('reverse',
+      {},
+      [List(a), List(a)],
+      function reverse(xs) {
+        if (_type(xs) === 'String') return reverse(xs.split('')).join('');
+        var result = [];
+        for (var idx = xs.length - 1; idx >= 0; idx -= 1) result.push(xs[idx]);
+        return result;
+      });
+
   //  ArrayLike :: TypeClass
   var ArrayLike = $.TypeClass(
     'ArrayLike',
diff --git a/test/reverse.js b/test/reverse.js
new file mode 100644
index 00000000..96a9cb34
--- /dev/null
+++ b/test/reverse.js
@@ -0,0 +1,43 @@
+'use strict';
+
+var throws = require('assert').throws;
+
+var eq = require('./utils').eq;
+var errorEq = require('./utils').errorEq;
+var S = require('..');
+
+
+describe('reverse', function() {
+
+  it('is a unary function', function() {
+    eq(typeof S.reverse, 'function');
+    eq(S.reverse.length, 1);
+  });
+
+  it('type checks its arguments', function() {
+    throws(function() { S.reverse({answer: 42}); },
+           errorEq(TypeError,
+                   'Invalid value\n' +
+                   '\n' +
+                   'reverse :: List a -> List a\n' +
+                   '           ^^^^^^\n' +
+                   '             1\n' +
+                   '\n' +
+                   '1)  {"answer": 42} :: Object, StrMap Number, StrMap FiniteNumber, StrMap NonZeroFiniteNumber, StrMap Integer, StrMap ValidNumber\n' +
+                   '\n' +
+                   'The value at position 1 is not a member of ‘List a’.\n'));
+
+  });
+
+  it('reverses arrays', function() {
+    eq(S.reverse([]), []);
+    eq(S.reverse([1, 2, 3]), [3, 2, 1]);
+    eq(S.reverse(['1', '2', '3']), ['3', '2', '1']);
+  });
+
+  it('reverses strings', function() {
+    eq(S.reverse(''), '');
+    eq(S.reverse('123'), '321');
+  });
+
+});