I am trying to call a Haskell function from an Eiffel program, using C as an intermediary. For starters, I compiled and ran a variation of the program shown in http://haskell.org/haskellwiki/Calling_Haskell_from_C, to make sure I had the C-code right. I then attempted to move it into Eiffel. I can compile the C code OK, but I'm running into problems with linking. I solved most of the problems by adding the -v flag to the call to ghc which I used to link the original (haskell + c only) program, and cut-and-paste the linker options from their into the Eiffel configuration file. This isn't really satisfactory - I would like some automatic way to determine what the flags should be. The remaining problem has me stumped. I am getting the following messages: big_file_C4_c.c:(.text+0x9f4f): undefined reference to `__stginit_Fib' /home/colin/fib/Fib_stub.o: In function `stginit_export_Fib_zdffibonaccizuhszuaQO': Fib_stub.c:(.text+0x5): undefined reference to `Fib_zdffibonaccizuhszuaQO_closure' /home/colin/fib/Fib_stub.o: In function `fibonacci_hs': Fib_stub.c:(.text+0x32): undefined reference to `Fib_zdffibonaccizuhszuaQO_closure' The Haskell code looks like this:
{-# LANGUAGE ForeignFunctionInterface #-}
module Fib where
import Foreign.C.Types import CString
fibonacci :: Int -> String fibonacci n = show (fibs !! n) where fibs = 0 : 1 : zipWith (+) fibs (tail fibs)
fibonacci_hs :: CInt -> IO CString fibonacci_hs = newCString . fibonacci . fromIntegral
foreign export ccall fibonacci_hs :: CInt -> IO CString
And the C code (in an Eiffel wrapper) looks like this:
haskell_fib (n: INTEGER): POINTER is
-- String representation of `n'th Fibonacci number as a string
external "C inline use