From e7cff009bf0c83e2ad260af969d60c26675f7a80 Mon Sep 17 00:00:00 2001
From: Adam Boniecki <adambonie@gmail.com>
Date: Sun, 19 Mar 2017 00:15:19 +0100
Subject: [PATCH] [WIP] Implement built-in function `next`

`next` implemented by trying to call `__next__` method of
passed object.
Implementation seems to be finished, but this is marked as
work in progress for now to investigate why few test cases
still fail (possibly due to a bug in new or existing code)
---
 batavia/builtins/next.js    | 29 ++++++++++++++++++++++++++++-
 tests/builtins/test_next.py | 20 +-------------------
 2 files changed, 29 insertions(+), 20 deletions(-)

diff --git a/batavia/builtins/next.js b/batavia/builtins/next.js
index 06795beed..162aa2034 100755
--- a/batavia/builtins/next.js
+++ b/batavia/builtins/next.js
@@ -1,9 +1,36 @@
 var exceptions = require('../core').exceptions
+var callables = require('../core').callables
+var type_name = require('../core').type_name
 
 function next(args, kwargs) {
     // if its iterable return next thing in iterable
     // else stop iteration
-    throw new exceptions.NotImplementedError.$pyclass("Builtin Batavia function 'next' not implemented")
+    if (arguments.length !== 2) {
+        throw new exceptions.BataviaError.$pyclass('Batavia calling convention not used.')
+    }
+    if (kwargs && Object.keys(kwargs).length > 0) {
+        throw new exceptions.TypeError.$pyclass('next() takes no keyword arguments')
+    }
+    if (!args || args.length === 0) {
+        throw new exceptions.TypeError.$pyclass('next expected at least 1 arguments, got 0')
+    }
+    if (args.length > 2) {
+        throw new exceptions.TypeError.$pyclass('next expected at most 2 arguments, got ' + args.length)
+    }
+
+    try {
+        return callables.call_method(args[0], '__next__', [])
+    } catch (e) {
+        if (e instanceof exceptions.StopIteration.$pyclass) {
+            if (args.length === 2) {
+                return args[1]
+            } else {
+                throw e
+            }
+        } else {
+            throw new exceptions.TypeError.$pyclass("'" + type_name(args[0]) + "' object is not an iterator")
+        }
+    }
 }
 next.__doc__ = 'next(iterator[, default])\n\nReturn the next item from the iterator. If default is given and the iterator\nis exhausted, it is returned instead of raising StopIteration.'
 
diff --git a/tests/builtins/test_next.py b/tests/builtins/test_next.py
index 460b84d2e..802dbc6f3 100644
--- a/tests/builtins/test_next.py
+++ b/tests/builtins/test_next.py
@@ -4,21 +4,19 @@
 
 
 class NextTests(TranspileTestCase):
-    @expectedFailure
+
     def test_next_success(self):
         self.assertCodeExecution("""
             i = iter([1])
             print(next(i))
         """)
 
-    @expectedFailure
     def test_next_success_with_default(self):
         self.assertCodeExecution("""
             i = iter([1])
             print(next(i, 0))
         """)
 
-    @expectedFailure
     def test_next_exhausted_with_default(self):
         self.assertCodeExecution("""
             i = iter([])
@@ -37,22 +35,6 @@ class BuiltinNextFunctionTests(BuiltinFunctionTestCase, TranspileTestCase):
     functions = ["next"]
 
     not_implemented = [
-        'test_noargs',
-        'test_bool',
-        'test_bytearray',
-        'test_bytes',
-        'test_class',
-        'test_complex',
-        'test_dict',
-        'test_float',
         'test_frozenset',
-        'test_int',
-        'test_list',
-        'test_None',
-        'test_NotImplemented',
-        'test_range',
         'test_set',
-        'test_slice',
-        'test_str',
-        'test_tuple',
     ]