Paul Keir wrote:
Hi All,
If I have an ADT, say
data T = A String Integer | B Double | C deriving(Eq)
and I want to find if a list (ts) of type T contains an element of subtype "B Double", must my "containsTypeX" function use a second "isTypeX" function as follows:
isTypeB :: T -> Bool isTypeB (B _) = True isTypeB _ = False
containsTypeB :: [T] -> Bool containsTypeB ts = maybe False (\x -> True) (find isTypeB ts)
Many other good posts have obviated the original question, but just to answer it directly. You can turn isTypeB into a lambda by using a case expression: isTypeB = \t -> case t of B _ -> True ; _ -> False And from there you can just inline the definition in order to remove isTypeB. Pattern matching in function definitions is just sugar for the case expression version, so this transformation is just what the compiler would be doing anyways. -- Live well, ~wren