CPP: Macros in Haskell

Question 1

What you are trying to do isn't quite possible, I don't think, when you define a macro in a hsc file it will get inlined into your generated .hs file, and if that macro calls .hsc macros.. well those won't be available anymore. The best you can do:

module Test where

import Foreign.Ptr
import Foreign.C.Types

data T
data Tn
data Ct

#opaque_t vector_T
#ccall create_std_vectorTn , IO (Ptr <vector_T>)
#ccall carray_to_std_vectorTn , Ptr Ct -> CSize -> IO (Ptr <vector_T>) 
#ccall std_vectorTn_to_carray , Ptr <vector_T> -> IO (Ptr Ct) 
#ccall std_vectorTn_length , Ptr <vector_T> -> IO CSize

If your C compiler knows where to find bindings.dsl.h then you should include it at the top; mine doesn't so I compile with hsc2hs --include=<path-to-bindings.dsl.h> test.hsc. This produces the following file:

{-# LINE 1 "test.hsc" #-}
module Test where
{-# LINE 2 "test.hsc" #-}

import Foreign.Ptr
import Foreign.C.Types

data T
data Tn
data Ct

data C'vector_T = C'vector_T

{-# LINE 11 "test.hsc" #-}
foreign import ccall "create_std_vectorTn" c'create_std_vectorTn
  :: IO (Ptr C'vector_T)
foreign import ccall "&create_std_vectorTn" p'create_std_vectorTn
  :: FunPtr (IO (Ptr C'vector_T))

{-# LINE 12 "test.hsc" #-}
foreign import ccall "carray_to_std_vectorTn" c'carray_to_std_vectorTn
  :: Ptr Ct -> CSize -> IO (Ptr C'vector_T)
foreign import ccall "&carray_to_std_vectorTn" p'carray_to_std_vectorTn
  :: FunPtr (Ptr Ct -> CSize -> IO (Ptr C'vector_T))

{-# LINE 13 "test.hsc" #-}
foreign import ccall "std_vectorTn_to_carray" c'std_vectorTn_to_carray
  :: Ptr C'vector_T -> IO (Ptr Ct)
foreign import ccall "&std_vectorTn_to_carray" p'std_vectorTn_to_carray
  :: FunPtr (Ptr C'vector_T -> IO (Ptr Ct))

{-# LINE 14 "test.hsc" #-}
foreign import ccall "std_vectorTn_length" c'std_vectorTn_length
  :: Ptr C'vector_T -> IO CSize
foreign import ccall "&std_vectorTn_length" p'std_vectorTn_length
  :: FunPtr (Ptr C'vector_T -> IO CSize)

{-# LINE 15 "test.hsc" #-}

So looks like defining your own macro is the way to go:

mymacro.h

#define hsc_declare_vector_funcs(t,tn,ct)\
  hsc_opaque_t(vector_##t)\
  hsc_ccall(create_std_vector##tn ,IO (Ptr <vector_##t>))\
  hsc_ccall(carray_to_std_vector##tn , Ptr ct -> CSize -> IO (Ptr <vector_##t>)) \
  hsc_ccall(std_vector##tn##_to_carray , Ptr <vector_##t> -> IO (Ptr ct)) \
  hsc_ccall(std_vector##tn##_length , Ptr <vector_##t> -> IO CSize)

test.hsc

module Test where

#include "mymacro.h"

import Foreign.Ptr
import Foreign.C.Types

#declare_vector_funcs int, i, CInt

test.hs

module Test where

import Foreign.Ptr
import Foreign.C.Types

data C'vector_int = C'vector_int
foreign import ccall "create_std_vectori" c'create_std_vectori
  :: IO (Ptr C'vector_int)
foreign import ccall "&create_std_vectori" p'create_std_vectori
  :: FunPtr (IO (Ptr C'vector_int))
foreign import ccall "carray_to_std_vectori" c'carray_to_std_vectori
  :: Ptr CInt -> CSize -> IO (Ptr C'vector_int)
foreign import ccall "&carray_to_std_vectori" p'carray_to_std_vectori
  :: FunPtr (Ptr CInt -> CSize -> IO (Ptr C'vector_int))
foreign import ccall "std_vectori_to_carray" c'std_vectori_to_carray
  :: Ptr C'vector_int -> IO (Ptr CInt)
foreign import ccall "&std_vectori_to_carray" p'std_vectori_to_carray
  :: FunPtr (Ptr C'vector_int -> IO (Ptr CInt))
foreign import ccall "std_vectori_length" c'std_vectori_length
  :: Ptr C'vector_int -> IO CSize
foreign import ccall "&std_vectori_length" p'std_vectori_length
  :: FunPtr (Ptr C'vector_int -> IO CSize)

Question 2

The following example compiles:

{-# LANGUAGE CPP #-}

#define MYMACRO 3
#define MAX(a,b) (if ((a) < (b)) \
              then (b) \
              else (a))

main = print $ show (MAX(MYMACRO,4) :: Int)

I need the parens around the code macro so that the following will (also) work:

main = print $ show MAX(MYMACRO,4)

Question 3

If you want to do that with bindings-DSL, take a look at how it was done in bindings-gobject. You have to use the hsc_* macros.

CPP: Macros in Haskell

New info.