On Tuesday, 2003-08-05, 15:22, CEST, Nick Name wrote:
[...]
Is there any way to parametrize a type by a value, rather than another type? What I would like to do is to define "list of length 3" and "list of length 4" as separate parametrization of the same type, such that I could write functions that accept lists (under my new typename) of any length as long as parameters have the same length. The goal is to remove the need for runtime checks all over the code.
This is called "dependent types" and is not a feature of haskell (nor of any language that I know); there was "cayenne" (try a google search) but I don't believe it is still mantained.
Well, there are, e.g., Ada and C++ which allow types to be parametrized by values. The point is that they obviously still use runtime checks, it's just that you don't have to code these checks explicitely.
BTW, why is there no general interest for such a thing as dependent types?
What negative consequences does their implementation have? I think, sometimes they could be quite handy.
V.
W. ;-)