The trick here is to use a type to represent the constraint rather than a class, if possible. Keean 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.
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?
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