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March 2011

2 participants
2 discussions

Possible to call Haskell function from C and return a struct by value?
by sframe 30 Mar '11

30 Mar '11

Greetings, I am a Haskell novice, but I have written some Haskell functions and would like to call them from C++. The functions perform world coordinate system conversions like the following: data Geocentric = Geocentric { ecefX :: Double, ecefY :: Double, ecefZ :: Double } deriving (Show) data Geodetic = Geodetic { latitude :: Double, longitude :: Double, height :: Double } deriving (Show) geocentricToGeodetic :: Geocentric -> Geodetic geocentricToGeodetic geocentric = Geodetic lat lon height where ... ... lat = ... lon = ... height = ... I would like to call these functions from C++ using FFI, and have figured out how to wrap using FFI to accept and return primitive types: xGeocentricFromGeodetic :: CDouble -> CDouble -> CDouble -> CDouble xGeocentricFromGeodetic lat lon height = realToFrac (ecefX (geodeticToGeocentric (Geodetic (realToFrac lat) (realToFrac lon) (realToFrac height)))) foreign export ccall xGeocentricFromGeodetic :: CDouble -> CDouble -> CDouble -> CDouble Would there be a way to accept a C struct and return a C struct by value, something like this: struct Geocentric { double ecefX; double ecefY; double ecefZ; }; struct Geodetic { double lat; double lon; double height; }; With a method like the following: Geocentric geocentricToGeodetic (const Geodetic & geod); I have investigated the Storable class, but it seems as though this is intended to be used with pointers. In addition, it seems that most of the examples I have found deal with calling C code from Haskell and not vice-versa. Does anyone know if this can be achieved, and if so how? Any help is much appreciated. -- View this message in context: http://haskell.1045720.n5.nabble.com/Possible-to-call-Haskell-function-from… Sent from the Haskell - FFI mailing list archive at Nabble.com.

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FFI, DLL Linking, Windows Haskell Platform 2010
by Nabil Alsharif 30 Mar '11

30 Mar '11

Hi Everybody, So, like every one else on this list, I have a C library that I would like to access form Haskell. I am in the process of writing a Haskell interface for the distorm3 disassembler. The library was compiled into a DLL using MSVC. Because this is the first I've used FFI I'm keeping it simple and there is only one function I import Ala: foreign import ccall "distorm.h distorm_version" c_distorm_version :: IO (CUInt) The issue is when I try to compile the library the linker goes haywire: C:\Users\tantalum\Documents\Research\distorm_test>ghc --make Main.hs [2 of 2] Compiling Main ( Main.hs, Main.o ) Linking Main.exe ... .\Distorm3.o:fake:(.text+0x11b): undefined reference to `distorm_version' collect2: ld returned 1 exit status C:\Users\tantalum\Documents\Research\distorm_test>ghc --make Main.hs -l distorm3 Linking Main.exe ... C:\Program Files (x86)\Haskell Platform\2010.2.0.0\mingw\bin\ld.exe: cannot find -lC:\Users\tantalum\AppData\Local\Temp\ghc5976_0\ghc5976_0.o collect2: ld returned 1 exit status Any ideas or suggestions? What is that temporary object file for? Thanks in advance for any help. Hope you all are having a good day. Nabil Alsharif.

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