On Tue, Sep 29, 2015, at 07:10 AM, jamb@hinojosa.com wrote:
* "Tree" is the name of the new type. * "Branch" and "Leaf" are the type constructors. * What is "a" and "b"?
"Tree" is not quite the name of a type. It is the name of a type constructor - in other words, it is a "type-level function". This also explains "a" and "b" - they are the parameters to the type constructor (which means they are "type variables"). To get a type, you have to apply the type constructor. So, for example, "Tree Char Int" is a type. "Branch" and "Leaf" are not type constructors - they are *data* constructors.
* It seems to me that this type is kind of "recursively" defined but I do not know exactly.
Yes. It's recursive because a value of type "Tree a b" can be built up from other values of type "Tree a b" (if you use the "Branch" constructor). -Karl