Slice.chs

{-# LANGUAGE ForeignFunctionInterface #-}

-- 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/>.

module CPython.Types.Slice
  ( Slice
  , sliceType
  , new
  , getIndices
  ) where

#include <hscpython-shim.h>

import           Prelude hiding (length)

import           CPython.Internal hiding (new)

newtype Slice = Slice (ForeignPtr Slice)

instance Object Slice where
  toObject (Slice x) = SomeObject x
  fromForeignPtr = Slice

instance Concrete Slice where
  concreteType _ = sliceType

{# fun pure unsafe hscpython_PySlice_Type as sliceType
  {} -> `Type' peekStaticObject* #}

-- | Return a new slice object with the given values. The /start/, /stop/,
-- and /step/ parameters are used as the values of the slice object
-- attributes of the same names. Any of the values may be 'Nothing', in which
-- case @None@ will be used for the corresponding attribute.
new :: (Object start, Object stop, Object step) => Maybe start -> Maybe stop -> Maybe step -> IO Slice
new start stop step =
  maybeWith withObject start $ \startPtr ->
  maybeWith withObject stop $ \stopPtr ->
  maybeWith withObject step $ \stepPtr ->
  {# call PySlice_New as ^ #} startPtr stopPtr stepPtr
  >>= stealObject

-- | Retrieve the start, stop, step, and slice length from a 'Slice',
-- assuming a sequence of the given length.
getIndices :: Slice
           -> Integer -- ^ Sequence length
           -> IO (Integer, Integer, Integer, Integer)
getIndices slice length =
  withObject slice $ \slicePtr ->
  let length' = fromIntegral length in
  alloca $ \startPtr ->
  alloca $ \stopPtr ->
  alloca $ \stepPtr ->
  alloca $ \sliceLenPtr -> do
  {# call PySlice_GetIndicesEx as ^ #}
    slicePtr length' startPtr stopPtr stepPtr sliceLenPtr
    >>= checkStatusCode
  start <- fmap toInteger $ peek startPtr
  stop <- fmap toInteger $ peek stopPtr
  step <- fmap toInteger $ peek stepPtr
  sliceLen <- fmap toInteger $ peek sliceLenPtr
  return (start, stop, step, sliceLen)