[Haskell-cafe] Matching constructors

Mark T.B. Carroll mark at ixod.org
Fri Feb 10 13:26:45 EST 2006


Creighton Hogg <wchogg at primula.hep.wisc.edu> 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 ]

y or z might be helpful.

-- Mark



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