That would need the FlexibleInstances extension though.
On 14-05-15 14:11, Kristof Bastiaensen wrote:
> Hi,
>
> Looking at the source code, it seems that virtual member functions are
> not supported yet by wxHaskell.
> I've been thinking about several solutions, and I have come up with a
> solution that seems reasonable:
>
> For example to subclass wxGridCellRenderer, define a typeclass
> gridCellRenderer and a newGridCellRenderer contructor:
>
> class WxGridCellRenderer where
> wxGridCellRendererDraw :: wxGrid a -> wxGridCellAttr
> <http://docs.wxwidgets.org/3.0/classwx_grid_cell_attr.html> -> wxDC
> <http://docs.wxwidgets.org/3.0/classwx_d_c.html> Rect
> <http://docs.wxwidgets.org/3.0/classwx_rect.html> -> Int -> Int ->
> Bool -> IO ()
> wxGridCellRendererDraw = wxGridCellRenderDrawDefault
> wxGridCellRendererGetBestSize :: (..)
> wxGridCellRendererGetBestSize = wxGridCellRendererGetBestSizeDefault
> (...)
>
> newGridCellRenderer :: (WxGridCellRenderer a) => IO a
>
> This creates a new gridCellRenderer, were the virtual functions call
> the functions in the instance.
>
> On the C side, create a subclass, with a constructor that takes the
> function definitions for all the virtual functions. The default
> definitions are simply the base class functions
> WxGridCellRenderer::Draw(), etc...
>
> It does need a lot of boilerplate, that may be automated via wxdirect.
>
> -- Kristof Bastiaensen
>
>
>
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