I think I got this idea from JHC, but I'm unable to find it documented in
the JHC manual at the moment. The idea is that when _ appears on the RHS of
an equation it is another name for undefined.
Here is a hypothetical example, inspired by code I've seen in FFI
definitions:
\begin{code}
{-# LANGUAGE EmptyDataDecls #-}
data Bar
instance Storable Bar where
sizeOf _ = sizeOf #{size struct Bar}
alignment _ = alignment (_ :: CDouble) -- here we could have just as
succinctly said alignment (1 :: CDouble)
data Foo -- the struct Foo on the C side contains a Bar
instance Storable Foo where
sizeOf _ = sizeOf #{size struct Foo}
alignment _ = alignment (_ :: Bar) -- we can't instantiate a Bar
\end{code}
Is this something people would be interested in having as an extension in
GHC? Or is it just too fluffy for anyone to really care?
Thanks,
Jason
_______________________________________________
Haskell-Cafe mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/haskell-cafe
