Hi Paul, maybe False (\x -> True) (find isTypeB ts) This can be more neatly expressed as: isJust (find isTypeB ts) But your entire thing can be expressed as: containsTypeB ts = any isTypeB ts I recommend reading through the Prelude interface and the List interface, it has many useful functions that will help. Thanks Neil ________________________________ From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Paul Keir Sent: 12 November 2008 10:09 am To: haskell-cafe@haskell.org Subject: [Haskell-cafe] Searching for ADT patterns with elem and find 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) I understand that while something like "find C ts" will work, "find (isTypeB _) ts" will not, but is there no such thing as a pattern combinator(?), or lambda that could help with this situation. I find I have many individual "isTypeB" functions now. Regards, Paul ============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ==============================================================================