Added reduce function

Author: amitayh

specs/lisp-spec.js

@@ -230,6 +230,18 @@ describe('lispjs', function () {
       assert.deepEqual(lisp.run(prog), [1, 3]);
     });
 
+    it('supports reduce', function () {
+      var prog = [
+        // Define some collection
+        ['define', 'coll', ['list', 1, 2, 3]],
+
+        // Sum numbers
+        ['reduce', 'coll', '+', 0]
+      ];
+
+      assert.equal(lisp.run(prog), 6);
+    });
+
     it('supports the Y-combinator', function () {
       var prog = [
         // Define the Y-combinator

src/env.js

@@ -112,6 +112,12 @@ var buildEnv = [
         ['cons', ['car', 'coll'], ['filter', 'pred', ['cdr', 'coll']]],
         ['filter', 'pred', ['cdr', 'coll']]]]],
 
+  // Reduce a collection
+  ['defun', 'reduce', ['coll', 'f', 'acc'],
+    ['if', ['empty', 'coll'],
+      'acc',
+      ['reduce', ['cdr', 'coll'], 'f', ['f', 'acc', ['car', 'coll']]]]],
+
   // Create a lexical scope with bound arguments and execute body in context
   ['defmacro', 'let', ['bindings', 'body'],
     ['concat',