Malcolm writes:

Bernie writes:

...

I did wonder how Hat tackled this. Out of curiosity what is the solution that Hat uses?

Hat doesn't have a solution. When the lack of correct defaulting causes Hat to generate type-incorrect code, the underlying compiler will complain vociferously. Our advice to users is to write `default ()' at the top of the module, then resolve the type errors they get from the normal compilation so that defaulting is completely eliminated. The code will then go through Hat smoothly.

It isn't very satisfactory, but in practice, defaulting doesn't really occur very often, so it isn't too much of a hardship.

That was going to be my fallback strategy, I'm glad I'm not the only one!

...

This adds an extra element of difficulty to the problem. I am trying my hardest to avoid needing the to import the original Prelude in a transformed module - this requires quite a bit of desugaring in the transformation.

For what reasons do you require the original prelude?

Exactly the same reasons. We want to do as little desugaring as necessary in the transformation, so inevitably we need at least a small part of the Prelude in scope.

I would like to use do-notation in the transformed program, but have it refer to Prelude.Monad and not MyPrelude.Monad which is also in scope. The reason I mention this is that the behviour of -fno-implicit-prelude seems to have changed with respect to desugaring do notation, at least according to this post from Simon Peyton-Jones: http://www.haskell.org/pipermail/glasgow-haskell-users/2002-July/003688.html In the upcoming 5.04 release you'll be able to do exactly that. GHC will use whatever >>= is in scope if you say -fno-implicit-prelude. Sure I can always get by without do notation, but the transformed program is then a lot uglier and harder to comprehend. Does hat work with ghc 5.04? Cheers, Bernie.