Is it possible to use list style pattern matching on vectors?
ie
import qualified Data.Vector as V
f :: V.Vector a -> a
f (x:xs) = x
gives an error
-XViewPatterns can let you do this:
{-# LANGUAGE ViewPatterns #-}
module VecViewPats where
import Data.Vector (Vector)
import qualified Data.Vector as V
uncons :: Vector a -> Maybe (a, Vector a)
uncons v = if V.null v
then Nothing
else Just (V.unsafeHead v, V.unsafeTail v)
vsum :: Num a => Vector a -> a
vsum (uncons -> Just (a,av)) = a + vsum av
vsum (uncons -> Nothing) = 0
Or -XLambdaCase
import Control.Category ((>>>))
-- ...
vsum :: Num a => Vector a -> a
vsum = uncons >>> \case
Just (a,av) -> a + vsum av
Nothing -> 0
But honestly, that's seems like a bit of a code smell as you're using one data structure (Vector) as another ([]) which suggests that maybe your choice of data structure is off.
If you really just want to treat it like a list for the purposes of some algorithm, why not use toList?
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