GHC bug,or Hugs feature?

[Malcolm Wallace]

Arthur Baars <arthurb@cs.uu.nl> writes:

> f :: a -> a
> f a | True         = a
>     | g 'a' == 'a' = g a
> 
> g :: a -> a
> g a | True         = a
>     | f 'a' == 'a' = f a
> 
> Is this a bug in GHC or a feature of Hugs?
> I did not check what NHC and other Haskell compilers say about this. Can
> someone try?

nhc98 agrees with GHC rather than Hugs.  The code above compiles fine.
If you omit one type signature, the error is

    Derived type for Test.f at 4:1 does not match due to:
        given free variable a is bound to Prelude.Char
    Derived:(Prelude.Char -> Prelude.Char)
    Given  :(a -> a)

If you omit both signatures, f and g are typed as Char->Char.
With or without type signatures, nhc98 additionally emits warnings:

    ======	Warning pattern removal:
    Alternative at 9:22 is hidden by alternative at 8:7
    Alternative at 5:22 is hidden by alternative at 4:7

Regards,
    Malcolm