[Haskell-cafe] A simple beginner question

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. Thanks, Adam