AW: AW: simulating dynamic dispatch

Thanks! These examples and counterexamples help a lot in understanding. Markus

The reason is that sum only works on integer lists, whereas the given type for fun requires that the first argument be a function that works on lists of any type, such as length. If sum were allowed as argument to fun, then we would also have to be allowed to say:

fun sum [True, False] [1,2]

which clearly makes no sense.

That Hugs refuses to report the type of fun has to with the fact that such (rank-2) types cannot be inferred. GHC generally has better support for higher-ranked types (no general inference, of course).

Hope that helped, Janis.

-- Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de