Re: [Haskell-cafe] FFI for a beginner

I think you should definitely use hsc2hs. It is simple to you use and would allow you to replace things like: peek ptr = do* a <- peekByteOff ptr 0 b <- peekByteOff ptr 4* return (MyStructType a b) By: #include "MyStruct.h" -- ^ Needs to be defined in a separate header peek ptr = do a <- (#peek MyStruct, foo) ptr b <- (#peek MyStruct, bar) ptr return (MyStructType a b) But I just know hsc2hs. Does c2hs automatically writes the Storable instances ? (Because it's kind of a daunting task...) 2011/4/12 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 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" 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 While the tutorials at HaskellWikihttp://www.haskell.org/haskellwiki/FFI_complete_examplesare helpful, they're outdated. Argh! The docshttp://www.haskell.org/ghc/docs/latest/html/users_guide/ffi-ghc.html#glasgow...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 hscharmhttps://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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