Dear List, Why does the first instance match? ANY is neither Eq nor Typeable. I thought I had some basic understanding of type classes, and now this... wojtek@biuro:~/src/he$ cat minimatch.hs {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE MultiParamTypeClasses #-} module MiniMatch where import Data.Typeable data A130 = A130 deriving (Eq) data ANY = ANY class AtmAcct a class Against q class (AtmAcct a, Against q) => Match a q where match :: a -> q -> Bool instance AtmAcct A130 instance Against ANY instance (Eq a, Eq q, Typeable a, Typeable q, AtmAcct a, Against q) => Match a q where match _ _ = False instance (AtmAcct a) => Match a ANY where match _ _ = True m1 = match A130 ANY -- offending line wojtek@biuro:~/src/he$ ghc minimatch.hs [1 of 1] Compiling MiniMatch ( minimatch.hs, minimatch.o ) minimatch.hs:21:6: error: • Overlapping instances for Match A130 ANY arising from a use of ‘match’ Matching instances: instance (Eq a, Eq q, Typeable a, Typeable q, AtmAcct a, Against q) => Match a q -- Defined at minimatch.hs:18:10 instance AtmAcct a => Match a ANY -- Defined at minimatch.hs:19:10 • In the expression: match A130 ANY In an equation for ‘m1’: m1 = match A130 ANY -- Thanks, Wojtek Narczyński