Strange behavior when using newtyped version of IO monad in FFI import declarations

Take a look at these two modules:

A.hs:

module A (GL) where

import Control.Monad
import Control.Monad.Trans

newtype GL a = GL (IO a) deriving (Functor, Monad, MonadIO)

B.hs:

module B where

import A

foreign import CALLCONV unsafe "glFlush" flush :: GL ()

Now, compile them with optimizations:

[david@alonzo temp]$ $HOME/ghc-6.10.1/bin/ghc A.hs B.hs -XGeneralizedNewtypeDeriving -XForeignFunctionInterface -DCALLCONV=ccall -XCPP -O
compilation IS NOT required
compilation IS NOT required
A.o:(.text+0x8e): undefined reference to `mtlzm1zi1zi0zi2_ControlziMonadziTrans_ZCDMonadIO_con_info'
A.o:(.text+0x237): undefined reference to `__stginit_mtlzm1zi1zi0zi2_ControlziMonadziTrans_'
B.o:(.text+0x1e): undefined reference to `glFlush'
/home/david/ghc-6.10.1//lib/ghc-6.10.1/libHSrts.a(Main.o): In function `real_main':
Main.c:(.text+0x12): undefined reference to `__stginit_ZCMain'
Main.c:(.text+0x26): undefined reference to `ZCMain_main_closure'
collect2: ld returnerade avslutningsstatus 1

It's OK - we pass the typechecking phase.

Now, see what happens when we compile without -O:

[david@alonzo temp]$ rm -f *.hi *.o
[david@alonzo temp]$ $HOME/ghc-6.10.1/bin/ghc A.hs B.hs -XGeneralizedNewtypeDeriving -XForeignFunctionInterface -DCALLCONV=ccall -XCPP

B.hs:5:0:
    Unacceptable result type in foreign declaration: GL ()
    When checking declaration:
        foreign import ccall unsafe "static  &glFlush" flush :: GL ()

Putting everything into one single module makes the type error go away completely (that is, also when compiling without -O).

Something strange must be going on.

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	david.waern@gmail.com
Operating system
Architecture