Re: [Haskell-beginners] a bunch o' questions
let t = Branch (Leaf 1) (Leaf 2) :: Tree Int you constuct a tree with two leaves, and after two colons say, that
Leaf and Branch are type-constructors, and "Tree a" is a parametrized type. Constructor is what you actually use to construct trees, but the type (Tree a) you use to annotate values. Like in the type of the tree is Tree Int Markus
Leaf and Branch are type-constructors, and "Tree a" is a parametrized type.
I think this is wrong. Leaf and Branch are *data* constructors, and Tree is, indeed, a type constructor.
From http://www.haskell.org/all_about_monads/html/meet.html :
Type constructors To understand monads in Haskell, you need to be comfortable dealing with type constructors. A type constructor is a parameterized type definition used with polymorphic types. By supplying a type constructor with one or more concrete types, you can construct a new concrete type in Haskell. In the definition of Maybe: data Maybe a = Nothing | Just a Maybe is a type constructor and Nothing and Just are data constructors. You can construct a data value by applying the Just data constructor to a value: country = Just "China" In the same way, you can construct a type by applying the Maybe type constructor to a type: lookupAge :: DB -> String -> Maybe Int Best regards, Ricardo Carnieri
Yep, your're right!
On Thu, Jul 1, 2010 at 7:49 PM, Ricardo Carnieri
Leaf and Branch are type-constructors, and "Tree a" is a parametrized type.
I think this is wrong. Leaf and Branch are *data* constructors, and Tree is, indeed, a type constructor.
participants (2)
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Markus Läll -
Ricardo Carnieri