Merge pull request #220 from gilligan/add-reverse

Add S.reverse

index.js

@@ -2460,6 +2460,28 @@
         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',

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');
+  });
+
+});