29 Jun
2012
29 Jun
'12
7:25 a.m.
class C a where
Hi, Is there a way to ensure that functions in a class instance are treated as top level definitions and not re-evaluated? For instance if I have this: list :: [a] instance List a => List [a] where list = permutations list <<< How can I ensure that list :: [[X]] is evaluated at most once for any type X (throughout my program)? I assume this is potentially harmful, since list can never be garbage collected and there may exist an unbounded number of X's. I currently have a solution that uses Typeable to memoise the result of the function based on its type. Is there an easier way? Regards, Jonas