[Haskell-cafe] FFI and modifying haskell memory

John Meacham john at repetae.net
Fri Oct 21 19:42:57 EDT 2005

On Fri, Oct 21, 2005 at 03:19:36PM +0100, Joel Reymont wrote:
> Is there a particular reason why StablePtr cannot provide a "fixed"  
> memory address? Then 4 bytes of memory won't need to be allocated so  
> that C could write to them and C could just modify the Haskell variable.

because haskell values don't have the same representation as C values.
haskell values are pointers to updatable thunks. in any case 'with'
just allocates 4 bytes on the stack (the same as a auto C declaration)
so is quite speedy compared to what it would take to make a haskell
value look like a C one. not to mention haskell values can't be

John Meacham - ⑆repetae.net⑆john⑈ 

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