{-# LANGUAGE CPP #-}
module Basement.Compat.ExtList
( length
, null
, sum
, reverse
, (!!)
) where
import Basement.Compat.Base
import Basement.Numerical.Additive
import Basement.Types.OffsetSize
import qualified GHC.List as List
length :: [a] -> CountOf a
#if MIN_VERSION_base(4,8,0)
length = CountOf . List.foldl' (\c _ -> c+1) 0
#else
length = CountOf . loop 0
where loop !acc [] = acc
loop !acc (_:xs) = loop (1+acc) xs
#endif
null :: [a] -> Bool
null [] = True
null (_:_) = False
sum :: Additive n => [n] -> n
sum [] = azero
sum (i:is) = loop i is
where
loop !acc [] = acc
loop !acc (x:xs) = loop (acc+x) xs
{-# INLINE loop #-}
reverse :: [a] -> [a]
reverse l = go l []
where
go [] acc = acc
go (x:xs) acc = go xs (x:acc)
(!!) :: [a] -> Offset a -> a
[] !! _ = error "invalid offset for !!"
(x:_) !! 0 = x
(_:xs) !! i = xs !! pred i