Re: [Haskell-cafe] A simple beginner question

adam.smyczek:

Example:

data SampleType = A | B Int | C String | D -- .... etc.

sampleTypes = [A, B 5, C "test"] :: [SampleType]

How do I find for example element A in the sampleTypes list? Do I have to create e.g.:

isA :: SampleType -> Bool isA A = True isA _ = False

for every constructor and use find? It feels like this is not the quicker method.

This is where the implicit filtering in a list comprehension comes in really handy, data T = A | B Int | C String | D deriving Show xs = [A, B 5, C "test", D] main = do print [ A | A <- xs ] -- filter A's print [ x | x@(C _) <- xs ] -- filter C's {- *Main> main [A] [C "test"] -}