Ensure fp.nthArg returns a curried function.

fp/_baseConvert.js

@@ -143,6 +143,7 @@ function baseConvert(util, name, func, options) {
     'keys': util.keys,
     'rearg': util.rearg,
     'spread': util.spread,
+    'toInteger': util.toInteger,
     'toPath': util.toPath
   };
 
@@ -156,6 +157,7 @@ function baseConvert(util, name, func, options) {
       keys = helpers.keys,
       rearg = helpers.rearg,
       spread = helpers.spread,
+      toInteger = helpers.toInteger,
       toPath = helpers.toPath;
 
   var aryMethodKeys = keys(mapping.aryMethod);
@@ -209,10 +211,16 @@ function baseConvert(util, name, func, options) {
         return func;
       };
     },
+    'nthArg': function(nthArg) {
+      return function(n) {
+        var arity = n < 0 ? 1 : (toInteger(n) + 1);
+        return curry(nthArg(n), arity);
+      };
+    },
     'rearg': function(rearg) {
       return function(func, indexes) {
-        var n = indexes ? indexes.length : 0;
-        return curry(rearg(func, indexes), n);
+        var arity = indexes ? indexes.length : 0;
+        return curry(rearg(func, indexes), arity);
       };
     },
     'runInContext': function(runInContext) {

fp/_mapping.js

@@ -73,10 +73,10 @@ exports.aryMethod = {
   '1': [
     'assignAll', 'assignInAll', 'attempt', 'castArray', 'ceil', 'create',
     'curry', 'curryRight', 'defaultsAll', 'defaultsDeepAll', 'floor', 'flow',
-    'flowRight', 'fromPairs', 'invert', 'iteratee', 'memoize', 'method',
-    'mergeAll', 'methodOf', 'mixin', 'over', 'overEvery', 'overSome', 'rest',
-    'reverse', 'round', 'runInContext', 'spread', 'template', 'trim', 'trimEnd',
-    'trimStart', 'uniqueId', 'words', 'zipAll'
+    'flowRight', 'fromPairs', 'invert', 'iteratee', 'memoize', 'method', 'mergeAll',
+    'methodOf', 'mixin', 'nthArg', 'over', 'overEvery', 'overSome','rest', 'reverse',
+    'round', 'runInContext', 'spread', 'template', 'trim', 'trimEnd', 'trimStart',
+    'uniqueId', 'words', 'zipAll'
   ],
   '2': [
     'add', 'after', 'ary', 'assign', 'assignAllWith', 'assignIn', 'assignInAllWith',

lib/fp/template/modules/_util.jst

@@ -10,5 +10,6 @@ module.exports = {
   'keys': require('../_baseKeys'),
   'rearg': require('../rearg'),
   'spread': require('../spread'),
+  'toInteger': require('../toInteger'),
   'toPath': require('../toPath')
 };

test/test-fp.js

@@ -371,7 +371,7 @@
         'method', 'methodOf', 'rest', 'runInContext'
       ];
 
-      var exceptions = funcMethods.concat('mixin', 'template'),
+      var exceptions = funcMethods.concat('mixin', 'nthArg', 'template'),
           expected = _.map(mapping.aryMethod[1], _.constant(true));
 
       var actual = _.map(mapping.aryMethod[1], function(methodName) {
@@ -1588,6 +1588,22 @@
 
   /*--------------------------------------------------------------------------*/
 
+  QUnit.module('fp.nthArg');
+
+  (function() {
+    QUnit.test('should return a curried function', function(assert) {
+      assert.expect(2);
+
+      var func = fp.nthArg(1);
+      assert.strictEqual(func(1)(2), 2);
+
+      func = fp.nthArg(-1);
+      assert.strictEqual(func(1), 1);
+    });
+  }());
+
+  /*--------------------------------------------------------------------------*/
+
   QUnit.module('fp.over');
 
   (function() {
@@ -1793,7 +1809,7 @@
       assert.deepEqual(rearged('c', 'a', 'b'), ['a', 'b', 'c']);
     });
 
-    QUnit.test('should curry the rearged function', function(assert) {
+    QUnit.test('should return a curried function', function(assert) {
       assert.expect(1);
 
       var rearged = fp.rearg([1, 2, 0], fn);