[Haskell-cafe] FFI Ptr Question

[Michael Jones]

I am having trouble figuring out how to pass callbacks to C.

Given the definition below it is not clear how to define a function and pass it. I tried:

getNumberOfRows :: CInt 
getNumberOfRows = 1

  table <- wxcGridTableCreate getNumberOfRows…

but the compiler barks at me:

src/MainGui.hs:577:32: Not in scope: data constructor ‘Ptr’

even through I do the imports:

import Foreign
import Foreign.C

There is also a _obj as the first value of wxcGridTableCreate and the callbacks, and I am not sure how to make a this* for it. I would have throughout that wxcGridTableCreate would return a Ptr.

The goal is to pass haskell functions into wxcGridTableCreate so the grid can call back to haskell.

Can someone show an example of just this one function, how to wrap a Ptr around it, and what to do with _obj?


DEFINITION

wxcGridTableCreate :: Ptr  a -> Ptr  b -> Ptr  c -> Ptr  d -> Ptr  e -> Ptr  f -> Ptr  g -> Ptr  h -> Ptr  i -> Ptr  j -> Ptr  k -> Ptr  l -> Ptr  m -> Ptr  n -> Ptr  o -> Ptr  p -> Ptr  q ->  IO (WXCGridTable  ())
wxcGridTableCreate _obj _EifGetNumberRows _EifGetNumberCols _EifGetValue _EifSetValue _EifIsEmptyCell _EifClear _EifInsertRows _EifAppendRows _EifDeleteRows _EifInsertCols _EifAppendCols _EifDeleteCols _EifSetRowLabelValue _EifSetColLabelValue _EifGetRowLabelValue _EifGetColLabelValue 
  = withObjectResult $
    wx_ELJGridTable_Create _obj  _EifGetNumberRows  _EifGetNumberCols  _EifGetValue  _EifSetValue  _EifIsEmptyCell  _EifClear  
    _EifInsertRows  _EifAppendRows  _EifDeleteRows  _EifInsertCols  _EifAppendCols  _EifDeleteCols  
    _EifSetRowLabelValue  _EifSetColLabelValue  _EifGetRowLabelValue  _EifGetColLabelValue  
foreign import ccall "ELJGridTable_Create" wx_ELJGridTable_Create :: Ptr  a -> Ptr  b -> Ptr  c -> Ptr  d -> Ptr  e -> Ptr  f -> Ptr  g -> Ptr  h -> Ptr  i -> Ptr  j -> Ptr  k -> Ptr  l -> Ptr  m -> Ptr  n -> Ptr  o -> Ptr  p -> Ptr  q -> IO (Ptr (TWXCGridTable ()))

typedef int   _cdecl (*TGridGetInt)(void* _obj);
typedef int   _cdecl (*TGridIsEmpty)(void* _obj, int row, int col);
typedef void* _cdecl (*TGridGetValue)(void* _obj, int row, int col);
typedef void  _cdecl (*TGridSetValue)(void* _obj, int row, int col, void* val);
typedef void  _cdecl (*TGridClear)(void* _obj);
typedef int   _cdecl (*TGridModify)(void* _obj, int pos, int num);
typedef int   _cdecl (*TGridMultiModify)(void* _obj, int num);
typedef void  _cdecl (*TGridSetLabel)(void* _obj, int idx, void* val);
typedef void* _cdecl (*TGridGetLabel)(void* _obj, int idx);

EWXWEXPORT(void*,ELJGridTable_Create)(void* self,void* _EifGetNumberRows,void* _EifGetNumberCols,void* _EifGetValue,void* _EifSetValue,void* _EifIsEmptyCell,void* _EifClear,void* _EifInsertRows,void* _EifAppendRows,void* _EifDeleteRows,void* _EifInsertCols,void* _EifAppendCols,void* _EifDeleteCols,void* _EifSetRowLabelValue,void* _EifSetColLabelValue,void* _EifGetRowLabelValue,void* _EifGetColLabelValue)
{
	return (void*)new ELJGridTable (self,