> The following program gives me a stack overflow for a file "big.tex"
> 150000 bytes long.
>
> -- Cut here --
> module Main where
>
> import Foreign.C.String
> import Foreign.Ptr
> import qualified GHC.IO
>
> main =
> do
> (ptr,len) <- GHC.IO.slurpFile "big.tex"
> peekCStringLen (castPtr ptr,len)
> return ()
> -- Cut here --
>
> The message is "Stack space overflow: current size 1048576 bytes."
>
> Could peekCStringLen be changed so it does not expect stack space
> proportionate to the input string? I use this method quite a lot
> for slurping strings in and out, so as it is the situation is
> inconvenient.
Yes, I've run into this before. In fact this is one of those tricky
problems where you can't quite get tail-recursion where you want it:
(pseudo-ish code follows)
peekCString ptr = do
x <- peek ptr
if x == '\0' then return [] else do
xs <- peekCString (ptr + 1)
return (x:xs)
Any ideas? I seem to recall the ML folks have a hack for dealing with
this.
One ugly solution that occurs to me is:
peekCString ptr = do
x <- peek ptr
if x == '\0' then return [] else do
return (x : unsafePerformIO (peekCString (ptr + 1))
and then do a deepSeq before returning the list (deepSeq is
tail-recursive). I'm sure there must be a cleverer solution - it has
that kind of smell about it.
Cheers,
Simon
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