Cagdas Ozgenc wrote:
From the previous discussion it has been brought to my attention that there is no much difference between
a -> b
and
data F a b = Blank a b -- "-> probably has a blank value constructor"
Therefore it should be trivial to define a label initialized to a function abstraction without using the -> type constructor. I mean
fun :: F Int Int fun ? = ?
now what do I write in place of 1st and 2nd question marks? Even if I can do this, how am I suppose to invoke fun so that it would yield an "Int" not a "F Int Int"?
The type constructor F and the type constructor (->) are quite different. They have the same kind, but just as the type only tell you part of what a value is, thekind only tells you part of what a type is. Very informally a value of type "F a b" means "I have an a and a b", whereas as type "a -> b" means "if you give me an a I'll give you a b". So the function arrow "consumes" its first argument rather than produces it.
Or maybe I should ask the following question: what would the "value constructor" of -> look like, theoretically?
Well, in Haskell it looks like "\ x -> e". It different from data type constructors in that it's a binding construct, but it's the thing that constructs objects in a function type. -- Lennart