c2hs in marshaller vs. gtk2hsC2hs

Question

i try to understand the difference between c2hs and gtk2hsC2hs (modified version of c2hs for use in gtk2hs). Consider the following coding:

module Matrix where

data Matrix = Matrix { xx :: !Double, yx :: !Double,
                       xy :: !Double, yy :: !Double,
                       x0 :: !Double, y0 :: !Double }
  deriving (Show, Eq) 

{#pointer *cairo_matrix_t as MatrixPtr -> Matrix#}

instance Storable Matrix where
    sizeOf _ = {#sizeof cairo_matrix_t#}
    alignment _ = alignment (undefined :: CDouble)
    peek p = do
        xx <- {#get cairo_matrix_t->xx#} p
        yx <- {#get cairo_matrix_t->yx#} p
        xy <- {#get cairo_matrix_t->xy#} p
        yy <- {#get cairo_matrix_t->yy#} p
        x0 <- {#get cairo_matrix_t->x0#} p
        y0 <- {#get cairo_matrix_t->y0#} p
        return $ Matrix (realToFrac xx) (realToFrac yx)
                (realToFrac xy) (realToFrac yy)
                (realToFrac x0) (realToFrac y0)

   poke p (Matrix xx yx xy yy x0 y0) = do
       {#set cairo_matrix_t->xx#} p (realToFrac xx)
       {#set cairo_matrix_t->yx#} p (realToFrac yx)
       {#set cairo_matrix_t->xy#} p (realToFrac xy)
       {#set cairo_matrix_t->yy#} p (realToFrac yy)
       {#set cairo_matrix_t->x0#} p (realToFrac x0)
       {#set cairo_matrix_t->y0#} p (realToFrac y0)
       return () 

{#context lib="cairo" #}

{#fun cairo_pattern_set_matrix as patternSetMatrix { unPattern `Pattern', `Matrix'} -> `()'#}
{#fun cairo_pattern_get_matrix as patternGetMatrix { unPattern `Pattern', alloca- `Matrix' peek*} -> `()'#}       

The second fun line (e.g. cairo_pattern_get_matrix) works for both tools (although the generated code is different), while the first (e.g. cairo_pattern_set_matrix) works only for gtk2hsC2hs.

The error message when using c2hs is:

Test.chs:35: (column 75) [ERROR]  >>> Missing "in" marshaller!
There is no default marshaller for this combination of Haskell and C type:
  Haskell type: Matrix
  C type      : (MatrixPtr)

I don't understand the problem here clearly, but from my point of view, this should be valid.

I use for c2hs:

C->Haskell Compiler, version 0.28.3 Switcheroo, 25 November 2017
  build platform is "x86_64-linux" <1, True, True, 1>

and gtk2hsC2hs:

C->Haskell Compiler, version 0.13.13 (gtk2hs branch) "Bin IO", 27 May 2012

Thanks in advance

Answer 1

Ok, the following seems to work:

{#fun cairo_pattern_set_matrix as patternSetMatrix 
        { `Pattern', with* `Matrix'} -> `()'#}

So the handling of newtype and in marshalers is different in c2hs and gtk2hsC2hs. I guess, this is because the latter is based on an ancient version.