2009/4/7 Michael Mossey
I'm coming from the OO world and trying to adapt.
me too :-)
For that matter, I don't know what the term is for a "StaffItem-type LayoutItem". The type is clearly LayoutItem. "StaffItem" is the constructor. How do you refer to the concept of a LayoutItem constructed via a StaffItem?
Again, StaffItem and TextItem resemble derived classes in OO.
To me, they are more close to C union : a data type than can alternatively have different structures, In your example, LayoutItem is a type name, while StaffItem and TextItem are constructor, that is functions. Saying that a function specializes a type is a bit of a stretch, I think ... Nevertheless, they can sometime be used to accomplish the same goal : where in OO you define an abstact class and then specialize with concrete classes to model a classification, in haskell you can define a data type with alternate constructors. I think that data types with alternate constructores are called algebraic data types in haskellese, but I'm not sure of that ...
Any clarification welcome. -Mike
Ciao ----- FB