[Haskell-cafe] FFI for a beginner

[Andrew Pennebaker]

hsc2hs and c2hs are good suggestions, and some of the tutorials I'm
following use them.

But 1) Many Haskell FFI tutorials don't require them, so they only seem to
help, or only help in older versions of GHC.

And 2) When I did compile using c2hs, it just produced the same file, but
with filler comments like {#- LINE 13 #-}. And they still refused to compile
for the same reason:

ld: duplicate symbol _Charm_getWidth_info in charm.o and charm.o

Cheers,

Andrew Pennebaker
www.yellosoft.us

On Sat, Apr 9, 2011 at 9:50 PM, Jason Dagit <dagitj at gmail.com> wrote:

> I don't know how to make ghc load them without using either hsc2hs or c2hs.
> I've had better experiences with hsc, but your mileage may vary.
>
> On Apr 8, 2011 3:34 AM, "Andrew Pennebaker" <andrew.pennebaker at gmail.com>
> wrote:
>
> ncurses is proving too difficult to setup, so I'm working on a new library
> called charm. The C code works by itself, but I can't compile a Haskell
> wrapper for it. While the tutorials at HaskellWiki<http://www.haskell.org/haskellwiki/FFI_complete_examples>are helpful, they're outdated. Argh! The
> docs<http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi-ghc.html#glasgow-foreign-headers>say that -#include pragmas no longer work, but fail to explain how to load
> code without them. Suffice to say I have no recourse but trial and error.
>
> GitHub: charm <https://github.com/mcandre/charm> and hscharm<https://github.com/mcandre/hscharm>
>
> <https://github.com/mcandre/charm>$ make
> cp /usr/include/charm.c .
> ghc --make -fforce-recomp -o hellocharm hellocharm.hs charm.hs charm.c
> -I/usr/include -dylib-install-name /usr/lib/libcharm.dynlib
> [1 of 2] Compiling Charm            ( charm.hs, charm.o )
> [2 of 2] Compiling Main             ( hellocharm.hs, hellocharm.o )
> Linking hellocharm ...
> ld: duplicate symbol _Charm_getWidth_info in charm.o and charm.o
> collect2: ld returned 1 exit status
> make: *** [hellocharm] Error 1
>
> Cheers,
>
> Andrew Pennebaker
> www.yellosoft.us
>
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