Changeset 2410 for Papers/polymorphic-variants-2012

Timestamp:

Oct 19, 2012, 5:05:55 PM (7 years ago)

Author:

mulligan

Message:

Changes to Section 2.

File:

• Papers/polymorphic-variants-2012/polymorphic-variants.tex (modified) (1 diff)

Papers/polymorphic-variants-2012/polymorphic-variants.tex

@@ -65 +65 @@
 We must introduce a new algebraic type with the additional constructor, lifting the old type---and any functions defined over it---into this type.
 
-Moving sideways, we can compare and contrast functional programming languages' use of algebraic data paired with pattern matching with the approach taken by object-oriented languages.
-In mainstream object-oriented languages such as Java algebraic data types correspond to class hierarchies, each constructor corresponding to a subclass in this hierarchy.
-Pattern matching is emulated using a dynamic dispatch mechanism.
-Using the object-oriented approach it is easy to add a new `case' to a given hierarchy: just introduce a new subclass.
+Moving sideways, we can compare and contrast functional programming languages' use of algebraic data paired with pattern matching with the approach taken by object-oriented languages, or extending the root object.
+In mainstream object-oriented languages such as Java algebraic data types correspond to interfaces, or some base object.
+Constructors correspond to classes implementing this interface; pattern matching is emulated using the language's dynamic dispatch mechanism.
+The interface specifies the permitted operations defined for the type.
+In contrast to the functional approach, it is hard to enlarge the set of operations defined over a given type without altering the entire class hierarchy.
+If the interface changes so must every class implementing it.
+However, note it is easy to extend the hierarchy to new cases, corresponding to the introduction of a new constructor in the functional world, by merely adding another class corresponding to that constructor implementing the interface.
 
 [dpm: reword the above --- hard to phrase precisely ]