[Haskell-cafe] A function that makes list of Bool lists from list of Int lists

Edward Z. Yang ezyang at MIT.EDU
Sat Apr 3 10:13:48 EDT 2010

Excerpts from Maur Toter's message of Sat Apr 03 09:54:26 -0400 2010:
> I am new with Haskell so I think this will be a pretty dumb question.
> I would like to make a function that makes this:
> listbool :: [[Int]] -> [[Bool]]
> in this way:
> listbool [[1,2],[3,4]] == [[True, True],[False, False]]
> listbool [[1],[5,5],[5,4],[2]] == [[True],[False, False],[True, True],
> [False]]
> So always True from the elements of the first list, False from the elements
> of the second one, etc...

Sure you can do this.  In fact, the type can be more general:

listbool :: [[a]] -> [[Bool]]
listbool xs = zipWith ($) (map (\x -> map (const x)) (cycle [True, False])) xs


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