Iterator.chs

-- Copyright (C) 2009 John Millikin <jmillikin@gmail.com>
-- 
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of the GNU General Public License as published by
-- the Free Software Foundation, either version 3 of the License, or
-- any later version.
-- 
-- This program is distributed in the hope that it will be useful,
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-- GNU General Public License for more details.
-- 
-- You should have received a copy of the GNU General Public License
-- along with this program.  If not, see <http://www.gnu.org/licenses/>.
-- 
{-# LANGUAGE ForeignFunctionInterface #-}
module CPython.Protocols.Iterator
	( Iterator (..)
	, SomeIterator
	, castToIterator
	, next
	) where
import CPython.Internal

#include <hscpython-shim.h>

-- | Attempt to convert an object to a generic 'Iterator'. If the object does
-- not implement the iterator protocol, returns 'Nothing'.
-- 
castToIterator :: Object a => a -> IO (Maybe SomeIterator)
castToIterator obj =
	withObject obj $ \objPtr -> do
	isIter <- fmap cToBool $ {# call hscpython_PyIter_Check as ^ #} objPtr
	return $ if isIter
		then Just $ unsafeCastToIterator obj
		else Nothing

-- | Return the next value from the iteration, or 'Nothing' if there are no
-- remaining items.
-- 
next :: Iterator iter => iter -> IO (Maybe SomeObject)
next iter =
	withObject iter $ \iterPtr -> do
	raw <- {# call PyIter_Next as ^ #} iterPtr
	if raw == nullPtr
		then do
			err <- {# call PyErr_Occurred as ^ #}
			exceptionIf $ err /= nullPtr
			return Nothing
		else fmap Just $ stealObject raw