On Sun, Oct 2, 2011 at 15:17, <sdiy...@sjtu.edu.cn> wrote: > But it's so verbose (even more so than similar C++ template code I guess), > introduces an additional name (the typeclass) into the current scope, and > requires 2 extensions: TypeFamilies and FlexibleInstances.Is there a cleaner > way to do this?
Not for your meaning of "clean". C++ is an object-oriented programming language; given a method call, it tries really hard to shoehorn the arguments to the call into some declared method somewhere along the inheritance chain. Haskell is a functional programming language; it is strongly typed, and typeclasses are a mechanism to allow that typing to be weakened in a strictly controlled fashion. In some sense, it's not *supposed* to be convenient, because the whole point is you're not supposed to throw arbitrarily-typed expressions at arbitrary functions. Instead, a properly designed program is characterized by its types; if the types are well designed for the problem being solved, they very nearly write the program by themselves. This doesn't mean that use of typeclasses / ad-hoc polymorphism is automatically a sign of a poor design, but it *does* mean you should think about what you're trying to do whenever you find yourself considering them. Nor does it mean that C++ is in some sense "wrong"; it means the languages are fundamentally different, and the appropriate design of a program is therefore also usually different between the two. -- brandon s allbery allber...@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms
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