Hi all, I have a type problem in my code which I dont know how to solve (and I'm not really sure why is caused). I have made a simplified example, can anyone have a look at it? Thanks in advance, The error is: Example.hs:24:47: Ambiguous type variable `a' in the constraint: `HDPrimType a' arising from use of `supplySig' at Example.hs:24:47-55 Probable fix: add a type signature that fixes these type variable(s) Here is the code --- module Example where data HDSignal a = HDSignal class HDPrimType a where class PortIndex a where class SourcePort s where -- Plug an external signal to the port plugSig :: (HDPrimType a, PortIndex ix) => ix -> s -> (HDSignal a -> b) -> b class DestPort d where -- Supply a signal to the port supplySig :: (PortIndex ix, HDPrimType a) => HDSignal a -> ix -> d -> d -- Connect providing indexes connectIx :: (SourcePort s, PortIndex six, DestPort d, PortIndex dix) => six -> s -> dix -> d -> d -- This can seem ugly, -- it would be easier for us having different types for plugSig and supplySig -- but the final user would find it much more difficult to deal with -- supplysig connectIx six s dix d = plugSig six s $ (push2 supplySig) dix d push2 :: (a -> b -> c -> d) -> b -> c -> a -> d push2 f = (\b c a -> f a b c)