Hi Andrew (Bromage), I reversed the parameter order to Data.Map.lookup and calling fromJust to pull out value from Maybe wrapper ... all as you suggested:
remLookupFwd :: (ReVars m t) => SimplRe t -> ReM m t (ReInfo t) remLookupFwd re = do fwd <- gets resFwdMap let { Just reinfo = fromJust(M.lookup re fwd) } -- PROBLEM return reinfo
I am still getting a type mismatch: Swish\HaskellRDF\Dfa\Dfa.lhs:162:29: Couldn't match expected type `Maybe t' against inferred type `ReInfo t1' In the expression: fromJust (M.lookup re fwd) In a pattern binding: Just reinfo = fromJust (M.lookup re fwd) In the expression: do fwd <- gets resFwdMap let Just reinfo = fromJust (M.lookup re fwd) return reinfo Vasili