[Haskell-cafe] Re: Matching constructors

Mark T.B. Carroll wrote:

Creighton Hogg writes:

...

data Patootie = Pa Int | Tootie Int and I want to pull out the indices of all elements of a list that have type constructor Tootie, how would I do that?

x = [Pa 3, Tootie 5, Pa 7, Tootie 9, Pa 11] y = [ i | Tootie i <- x ] z = [ i | i@(Tootie _) <- x ]

I think this is what the OP wanted: [ i | (i,Tootie _) <- zip [0..] x ] -- Ben