gistfile1.txt

[1 of 1] Compiling VV               ( test.hs, test.o )

test.hs:17:57:
    Could not deduce (Storable a0) arising from a use of `sizeOf'
    from the context (Num a, Storable a)
      bound by the type signature for
                 loadVector :: (Num a, Storable a) => String -> IO (U.Vector a)
      at test.hs:11:15-62
    The type variable `a0' is ambiguous
    Possible fix: add a type signature that fixes these type variable(s)
    Note: there are several potential instances:
      instance Storable Bool -- Defined in `Foreign.Storable'
      instance Storable Char -- Defined in `Foreign.Storable'
      instance Storable Double -- Defined in `Foreign.Storable'
      ...plus 15 others
    In the second argument of `div', namely `sizeOf (0 :: a)'
    In the second argument of `U.unsafeFromForeignPtr0', namely
      `(len `div` sizeOf (0 :: a))'
    In the second argument of `($)', namely
      `U.unsafeFromForeignPtr0 ptr (len `div` sizeOf (0 :: a))'

test.hs:17:65:
    Could not deduce (Num a1) arising from the literal `0'
    from the context (Num a, Storable a)
      bound by the type signature for
                 loadVector :: (Num a, Storable a) => String -> IO (U.Vector a)
      at test.hs:11:15-62
    Possible fix:
      add (Num a1) to the context of
        an expression type signature: a1
        or the type signature for
             loadVector :: (Num a, Storable a) => String -> IO (U.Vector a)
    In the first argument of `sizeOf', namely `(0 :: a)'
    In the second argument of `div', namely `sizeOf (0 :: a)'
    In the second argument of `U.unsafeFromForeignPtr0', namely
      `(len `div` sizeOf (0 :: a))'

VV.hs

{-# LANGUAGE ScopedTypeVariables #-}
module VV where

import Control.Monad
import Foreign.ForeignPtr.Safe
import Foreign.Storable
import System.IO
import qualified Data.Vector.Storable as U


loadVector :: (Num a, Storable a) => String -> IO (U.Vector a)
loadVector name =
    withFile name ReadMode $ \h -> do
        len <- liftM fromIntegral $ hFileSize h
        ptr <- mallocForeignPtrBytes len
        _ <- withForeignPtr ptr $ \p -> hGetBuf h p len
        return $ U.unsafeFromForeignPtr0 ptr (len `div` sizeOf (0::a))