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bundled/Basement/Compat/ExtList.hs

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+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE RebindableSyntax #-}
+{-# LANGUAGE NoImplicitPrelude #-}
+{-# 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
+
+-- | Compute the size of the 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 the element in a list
+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