Ian Lynagh wrote:
undecidable instances are marked "probably no" for Haskell'.
which, btw, I think is a bad idea. I had really hoped that Haskell' would sort
out the differences and standardize the behaviour of such common extensions.
not standardizing them won't make them go away, nor will they suddenly
cease to be useful. they will just keep causing problems because implementations
interpret them differently.. but I lost that argument long ago.
The bottom line is that the instance:
instance (MonadTrans t, MonadCGI m, Monad (t m)) => MonadCGI (t m) where
needs both overlapping and undecidable instances, doesn't work in
Hugs, and probably won't be Haskell'-compatible.
but overlapping instances were also pioneered in Hugs!-)
there are differences, eg, in how FDs combine with overlaps, or how scoped
type variables in instances are interpreted, but Hugs has both unlimited and
overlapping instances.
so the problem has to lie elsewhere..
claus
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