10 Mar
2007
10 Mar
'07
2:52 p.m.
I'm pretty sure you can define a catamorphism for any regular algebraic data type.
Actually, so-called negative occurrences in (regular) data types cause problems. Try to define the catamorphism of data Exp = Num Int | Lam (Exp -> Exp) | App Exp Exp to see the problem, Stefan