53 lines
1.1 KiB
Haskell
53 lines
1.1 KiB
Haskell
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{-# LANGUAGE BangPatterns #-}
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{-# LANGUAGE DeriveDataTypeable #-}
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{-# LANGUAGE TypeFamilies #-}
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{-# LANGUAGE RebindableSyntax #-}
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{-# LANGUAGE NoImplicitPrelude #-}
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{-# LANGUAGE CPP #-}
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module Basement.Compat.ExtList
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( length
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, null
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, sum
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, reverse
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, (!!)
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) where
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import Basement.Compat.Base
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import Basement.Numerical.Additive
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import Basement.Types.OffsetSize
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import qualified GHC.List as List
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-- | Compute the size of the list
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length :: [a] -> CountOf a
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#if MIN_VERSION_base(4,8,0)
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length = CountOf . List.foldl' (\c _ -> c+1) 0
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#else
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length = CountOf . loop 0
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where loop !acc [] = acc
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loop !acc (_:xs) = loop (1+acc) xs
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#endif
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null :: [a] -> Bool
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null [] = True
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null (_:_) = False
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-- | Sum the element in a list
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sum :: Additive n => [n] -> n
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sum [] = azero
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sum (i:is) = loop i is
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where
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loop !acc [] = acc
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loop !acc (x:xs) = loop (acc+x) xs
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{-# INLINE loop #-}
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reverse :: [a] -> [a]
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reverse l = go l []
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where
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go [] acc = acc
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go (x:xs) acc = go xs (x:acc)
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(!!) :: [a] -> Offset a -> a
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[] !! _ = error "invalid offset for !!"
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(x:_) !! 0 = x
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(_:xs) !! i = xs !! pred i
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