FFI docs

Manuel M T Chakravarty chak at cse.unsw.edu.au
Sat Apr 15 16:04:30 EDT 2006


I started to collect all pending issues concerning the FFI spec on the
H' wiki page for the FFI:


There is also another issue concerning newtypes that SimonM brought up a while ago.


> A couple of comments about the FFI spec.
> I was trying to find out whether the automatic newtype unwrapping for
> 'foreign' declarations was part of the FFI spec.  I searched for
> 'newtype'.  Nothing.
> Turns out that the *only* reference is in the sentence in 3.2:
> 	"The argument types ati produced by fatype must be marshallable
> foreign types; that is, each
> ati is either (1) a basic foreign type or (2) a type synonym or renamed
> datatype of a marshallable
> foreign type."
> This is very quiet!  The "renamed datatype" nomenclature is never used
> in practice (only in the Haskell report), and in any case the sentence
> is hard to unpick without an example or two.
> Second point.  Consider
> 	foreign import "dynamic" foo :: (Int -> IO Int) -> ...
> I'm not sure whether (Int -> IO Int) is considered a "marshallable
> foreign type", according to the defn in 3.2. 
> I also found the separation of 4.1.3 from 3.2 quite hard to understand.
> I was searching in 3.2 for "wrapper" and "dynamic" in vain!  I don't
> have a good solution to this, except perhaps some explicit fwd refs, and
> a clear explanation of the logic behind the structure of the document.
> Since some aspects of the FFI spec may change slightly for Haskell',
> this seemed like a good moment to mention these points.
> Simon
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