Re: [Haskell-cafe] Problem with overlapping class instances

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. Ralf 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?