27 Oct
2005
27 Oct
'05
2:56 p.m.
Tom Hawkins wrote:
In a pure language, is it possible to detect cycles in recursive data structures? For example, is it possible to determine that "cyclic" has a loop? ...
data Expr = Constant Int | Addition Expr Expr
cyclic :: Expr cyclic = Addition (Constant 1) cyclic
Or phased differently, is it possible to make "Expr" an instance of "Eq" such that cyclic == cyclic is smart enough to avoid a recursive decent?
No. And there is nothing that says that your definition of cyclic will actually have a cycle in the implementation. -- Lennart