6 Dec
2001
6 Dec
'01
9:16 p.m.
On Friday 30 November 2001 03:03 am, Josef Svenningsson wrote:
Hi!
It seems as the functional dependencies are not working as well as they should.
Suppose I have the following class:
\begin{code} class A a b | a -> b where foo :: a b \end{code}
and then I declare the following type:
\begin{code} newtype Foo = Bar (forall a b. A a b => a Int) \end{code}
Loading this in hugs gives the following error message: ERROR HugsBug.lhs:9 - Ambiguous type signature in type component *** ambiguous type : A a b => a Int
But the type is clearly not ambiguous since the functional dependency determines b whenever a is known.
Hugs is a bit overly aggressive there about warning of potential ambiguity. This is fixed in the upcoming release. --Jeff