Re: [Haskell-cafe] Newbie: generating a truth table

One possible way to generate the values would be using a generic function for permutation with repetition, such as: permuteRep :: [a] -> [b] -> [[(a,b)]] permuteRep [] _ = [] permuteRep (a:[]) bs = [ [ (a,b) ] | b <- bs ] permuteRep (a:as) bs = concat [ [ (a,b):p | p <- permuteRep as bs ] | b <- bs ] and then use: lines = permuteRep ["x","y","z"] [False,True] In case the variable names can be discarded (or, in this case, not generated ... lazy evaluation rox ;-), then: map (map snd) lines This avoids having to provide a "domain" for each variable in the list comprehension, which could be problematic when dealing with many variables On 2/21/07, Joe Thornber wrote:

...

On 2/10/07, Peter Berry wrote: Prelude> putStrLn $ concatMap (flip (++)"\n") $ map show $ [(x,y,(&&) x y) |x <- [True,False],y <- [True,False]]

This can be simplified slightly to:

Prelude > putStrLn . unlines . map show $ [(x, y, x && y) | x <- [True, False], y <- [True, False]]

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