[C2hs] Marshal Haskell list into monolithic arrays

[Duncan Coutts]

On Thu, 2006-08-17 at 21:49 +0000, zhu Jun wrote:
> I freed 'mfs' and 'fsP2' before return also.
> 
> >lowPassFilter :: [CFloat] -> CFloat
> >lowPassFilter fs =  (unsafePerformIO (lowPassFilterWrap fs))
> >    where lowPassFilterWrap :: [CFloat] -> IO CFloat
> >	  lowPassFilterWrap fs = do
> >	        mfs <- newArray fs
> >                fsP2 <- malloc
> >                r <- f_lowPassFilter mfs fsP2
> >                returnF <- peek fsP2
> >                free mfs
> >                free fsP2
> >                return returnF

By the way, instead of using this pattern:

thing <- malloc
...
free thing

you can use the with* style functions:

alloca $ \thing -> do
  ...

because that automatically deals with free, so you don't forget. It also
deals with freeing even if there is an exception.

See the documentation for the various Foreign.* modules:

http://haskell.org/ghc/docs/latest/html/libraries/base/Foreign-Marshal-Alloc.html
http://haskell.org/ghc/docs/latest/html/libraries/base/Foreign-Marshal-Array.html

In your case you might replace newArray and malloc by withArray and
alloca.

Duncan