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
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