On Thu, 2007-08-30 at 23:58 +0200, jerzy.karczmarczuk@info.unicaen.fr wrote:
Dan Piponi writes:
In mathematics, if you write "x = f y" you mean that these two expressions are equal. In Haskell, if you say "x = f y" you mean *make* then equal!
Haskell is a declarative language, not an imperative language. When you write "x = f x" in Haskell, you're declaring to the compiler that x equals f x. In an imperative language like Java, the line x = f(x) gives the compiler the imperative to emit instructions to store the value of f(x) in a 'box' called x. In Haskell, there is no box.
Well, there are boxes... But there also thunks and latent, yet-unevaluated graphs...
Anyway, I believe strongly that ALL people who have problems with the Haskell protocole, and they are numerous, I teach a good sample of them, should be encouraged to learn Prolog. IN DEPTH, and I mean it, Andrew Coppin and Peter Hercek !
In Prolog A=B is the unification, which is a bit more than equality, and something much more aggressive than an assignment. When you REALLY understand unification, it will be easier to see the lazy instantiation of the Haskell assignment, and, additionally, it becomes much more easy to understand the automatic inference of types, which sooner or later must be harnessed by all Haskell programmers...
One should learn Prolog anyway.