Merge pull request #811 from null-a/repeat-arg-check

Add argument checks to repeat function

src/header.wppl

@@ -384,17 +384,22 @@ var groupBy = function(cmp, ar) {
 
 var repeat = function(n, fn) {
   var helper = function(m) {
-    if (m == 0) {
+    if (m === 0) {
       return [];
-    } else if (m == 1) {
+    } else if (m === 1) {
       return [fn()];
     } else {
       var m1 = Math.ceil(m / 2),
           m2 = m - m1;
       return helper(m1).concat(helper(m2));
     }
   }
-
+  if (!util.isInteger(n) || n < 0) {
+    error('Expected first argument to be a non-negative integer.');
+  }
+  if (!_.isFunction(fn)) {
+    error('Expected second argument to be a function.');
+  }
   return helper(n);
 }