2009/4/7 Michael Mossey <mpm@alumni.caltech.edu>

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

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