[Haskell-cafe] Problems with type families

Silvio Frischknecht silvio.frischi at gmail.com
Mon Jul 6 19:03:10 UTC 2015

What's the error message? Is a bit hard without that.

The problem is probably that you have to explicitly state everything.


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.


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