-----Original Message----- From: Alastair Reid [mailto:reid@reid-consulting-uk.ltd.uk] Sent: 02 July 2002 18:34 To: Ian Lynagh Cc: ffi@haskell.org Subject: Re: More C interfacing issues

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Firstly, some ncurses calls return a *WINDOW and others take one as an argument but you never actually look at the contents of one yourself. I have defined "data Window = Window" and am using Ptr Window for the types of these. However, this means I get a warning about an unused constructor. Is there a better way to do this?

Hugs supports:

data Window

and I believe GHC and NHC do too. (Malcolm, SimonM: please shout if I overstate.)

Yes, GHC does.

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Secondly, does anyone have any suggestions on how to provide an interface to this?

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void getyx(WINDOW *win, int y, int x);

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The getyx macro places the current cursor position of the given window in the two integer variables y and x.

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The type would probably ideally be "Ptr Window -> IO (CInt, CInt)".

The easy way is to use GreenCard (the other ffi frontends may be of use too).

Or, you can do what GreenCard does which is to add 3 wrapper functions more or less like this:

What's wrong with just doing this in the plain FFI? data Window foreign import ccall "getyx" getyx :: Ptr Window -> Ptr CInt -> Ptr CInt -> IO () niceGetYX :: Ptr Window -> IO (CInt, CInt) niceGetYX win = alloca $ \py -> alloca $ \px -> do getyx win py px y <- peek py x <- peek px return (x,y) Have I missed something? Cheers, Simon