master caster

[tiedyedave]

From Pierce's Types and Programming Languages:

"There are three rules for type casts: in an upcast the subject is a subclass of the target, in a downcast the target is a subclass of the subject, and in a stupid cast the target is unrelated to the subject."

Comments

Re: special guest replier!

[rjmccall.livejournal.com]

That's not bad; I hadn't considered making case part of the signature, but it's clearly the sensible move. Maybe a record type instead of a curried list, since ordering is a bit arbitrary -- so, in SML syntax:

datatype foo = bar of X | baz of Y
val case: { bar: X -> 'a, baz: Y -> 'a } -> foo -> 'a