Yes, this does help, thank you. I didn't know you could generate
specialized instances. In fact, I was so sure that this was some
arcane feature I immediately went to the GHC User Guide because I
didn't believe it was documented.
I immediately stumbled upon Section 8.13.9.
Thanks to everyone who helped me with this. I think I've achieved a
small bit of enlightenment.
Cheers,
John
On Fri, Nov 28, 2008 at 2:46 PM, Simon Peyton-Jones
<[EMAIL PROTECTED]> wrote:
> The $f2 comes from the instance Monad (IterateeGM ...).
> print_lines uses a specialised version of that instance, namely
> Monad (IterateeGM el IO)
> The fact that print_lines uses it makes GHC generate a specialised version of
> the instance decl.
>
> Even in the absence of print_lines you can generate the specialised instance
> thus
>
> instance Monad m => Monad (IterateeGM el m) where
> {-# SPECIALISE instance Monad (IterateeGM el IO) #-}
> ... methods...
>
> does that help?
>
> Simon
>
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