On 9/14/07, Jules Bean <[EMAIL PROTECTED]> wrote:
> > {-# OPTIONS -fglasgow-exts #-}
>
> (extensions are only for deriving (Monad), it's not important)
If that's the case, you should be able to write (assuming GHC 6.6+)
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
though I don't know how well other implementations support it.
> Incidentally, I don't believe this technique has any performance
> implication at all. The newtypes are all erased at compile time.
One potential slowdown is the added typeclass polymorphism (for
MonadGL); hopefully the compiler is clever enough to eliminate
dictionary passing/lookup.
> Any comments? I'm sure this has been shown before but I don't
> remember where.
I'm not aware of any GL-specific explanation, but I think the trick of
using monad classes as a capability system has been around for a
while. (In the "folklore", you might say.)
Using classes for transparent lifting seems to come up in discussions
of the standard library's I/O functions. Writing "liftIO" everywhere
is just as painful as "runGL".
Stuart
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