[Haskell-cafe] Problem with overlapping class instances
gk at ninebynine.org
Tue Nov 23 04:31:38 EST 2004
At 21:40 22/11/04 +0100, Ralf Laemmel wrote:
>Instance selection and thereby overlapping resolution
>is *independent* of constraints. It is defined to be purely
>syntactical in terms of instance heads. See the HList paper
>for some weird examples.
That explains it. Thanks!
>Graham Klyne wrote:
>>The reported overlapping instance is [Char], which I take to be derived
>>from the type constructor  applied to type Char, this yielding a form
>>that matches (cw c). But the instance ConceptExpr (cw c) is declared to
>>be dependent on the context ConceptWrapper cw c, which has *not* been
>>declared for the type constructor .
>>GHCi with -fglasgow-exts is no more informative.
>>What am I missing here?
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