Linker error with FFI

[konsumlamm]

I'm currently modifying binary to work with MicroHs (see haskell/binary#237). However, when compiling the following example program

import Control.Applicative

import Data.Binary
import Data.Word

data Exp = IntE Int | OpE String Exp Exp deriving (Show)

instance Binary Exp where
    put (IntE i) = do
        put (0 :: Word8)
        put i
    put (OpE s e1 e2) = do
        put (1 :: Word8)
        put s
        put e1
        put e2

    get = do
        t <- get :: Get Word8
        case t of
            0 -> fmap IntE get
            1 -> liftA3 OpE get get get

main :: IO ()
main = do
    let bs = encode $ OpE "*" (IntE 7) (OpE "/" (IntE 4) (IntE 2))
    print bs
    print (decode bs :: Exp)

I get a linker error:

/usr/bin/ld: /tmp/ccnVdbAP.o: in function `xhs_free_stable_ptr':
mhsc254JJv.c:(.text+0x30): multiple definition of `xhs_free_stable_ptr'; /tmp/ccnW2rkp.o:unaligned_read.c:(.text+0x0): first defined here
/usr/bin/ld: /tmp/ccnVdbAP.o: in function `hs_free_fun_ptr':
mhsc254JJv.c:(.text+0x40): multiple definition of `hs_free_fun_ptr'; /tmp/ccnW2rkp.o:unaligned_read.c:(.text+0x10): first defined here

xhs_free_stable_ptr and hs_free_fun_ptr are defined in HsFFI.h, which has a #pragma once, so it shouldn't be included more than once.

[konsumlamm]

So apparently #pragma once only prevents HsFFI.h from being included more than once per compilation unit. Having multiple compilation units that include it results in multiple definitions.

[augustss]

I;ve moved the function definitions to eval.c, where they belong.