[Haskell-cafe] [Haskell-Cafe] Different memory profile in cabal project.

[Thomas Vanhelden]

I have a (dummy) program that reads the contents of a file into a ByteString and then converts the ByteString to a Vector of Floats. To test the laziness of this program,  I’ve taken a slice of the the Vector and printed it to the standard output.

The program looks like this:

	import qualified Data.Vector.Unboxed as V
	import qualified Data.ByteString as BS
	import Data.Word
	import System.Environment
	import GHC.Int

	main = do
    		[file] <- getArgs
    		samples <- getSamplesFromFile file
    		let slice = V.slice 0 50000 samples
    		print slice
	
	getSamplesFromFile = fmap toVector . BS.readFile 

	toVector :: BS.ByteString -> V.Vector Float
	toVector bs =  vgenerate (fromIntegral (BS.length bs `div` 3)) $ \i ->
	     	myToFloat [BS.index bs (3*i), BS.index bs (3*i+1), BS.index bs (3*i+2)]
	   where
 	  	 myToFloat :: [Word8] -> Float
  	  	 myToFloat = sum . map fromIntegral 

	vgenerate n f = V.generate n (f . fromIntegral)


So I compile this program and generate a memory profile via:
ghc Main.hs -O2 -rtsopts -prof 
./Main debug48.wav +RTS -hy
hp2ps -e8in -c Main.hp
ps2pdf Main.ps
The file debug48.wav  is a 12.9MB file.
This is the result:





If I now create a cabal project and add the exact same program as the main file by:
mkdir testing
cd testing
cabal init
add the program’s code to src/Main.hs
add bytestring and vector to the build dependencies (in testing.cabal)
add -O2 -rtsopts -prof to the ghc-options (in testing.cabal)
cabal install
testing debug48.wav +RTS -hy
hp2ps -e8in -c testing.hp
ps2pdf testing.ps
This is the result:



How can there be such a big difference in memory usage, just by the code being part of a cabal project?
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