Hello folks, Could somebody explain what a coverage condition is and what this error message means.. "Illegal instance declaration for 'GT (GT2 map1 map2) (k1,k2)' (the Coverage Condition fails for one of the functional dependencies) In the instance declaration for 'GT (GT2 map1 map2) (k1,k2)'" The offending code looks like this..
-- Generalsed Trie map class class Ord k => GT map k | map -> k , k -> map where
-- Map type for pairs newtype (GT2 map1 map2 a) = GT2 (map1 (map2 a))
-- Which is an instance of GT instance (GT map1 k1, GT map2 k2) => GT (GT2 map1 map2) (k1,k2) where
This is with ghc 6.6. The strange thing is this code used to compile fine with earlier versions (but I don't know if it actually worked because I never tested it). Thanks -- Adrian Hey