Re: [Haskell-cafe] Problems with type families

What's the error message? Is a bit hard without that. The problem is probably that you have to explicitly state everything. Maybe TFunIn (ComposeT t1 t2) e ~ TFunOut (SignalT t2 e) The problem with typefamilies is that often things can not be used as you would expect unless you state things explicitly. It is because the instance declaration can not know that TFunIn is always the same. You could import two different ones from different modules and thus convert one type into another. closed typefamilies can sometimes help too. Silvio