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

It would be better to produce a triple (as was suggested) loop = [(x, y, x&&y) | x <- [True, False], y <- [True, False]] The you can map a function that prints over that. Or even better map a function that generates the strings, and the use one big putStr at the end. Always try to separate IO from computation. -- Lennart On Feb 6, 2007, at 10:18 , phiroc@free.fr wrote:

Ketil,

thanks for you help.

Here's the code:

and2 :: Bool -> Bool -> Bool and2 a b = a && b

loop = [ and2 x y | x <- [True,False], y <- [True,False] ]

Now, how do I have Haskell print

printStrLn("True and True = ") + <result of calling and2 True True> printStrLn("True and False = ") + <result of calling and2 True False> ...

Thanks.

phiroc

Quoting Ketil Malde :

...

phiroc@free.fr wrote:

...

I would like to create a Haskell function that generates a truth table, for all Boolean values, say, using the following "and" function :

and :: Bool -> Bool -> Bool and a b = a && b

What is the type of the resulting table?

...

I have tried creating a second function called "loop", which repeatedly calls "and", but it did not work, because, for some reason unknown to me, "do" does not like repeated function calls

loop = do and True True and True False

I'm not sure I understand what you expected here. The 'do' syntax is for monadic code.

...

Is there a better way to repeatedly call "and"?

If you want your table in list for, I'd suggest using a list comprehension.

Here's how you'd calculate squares of numbers, for instance:

squares = [ x^2 | x <- [1..5] ]

...

Furthermore, is there a way in Haskell to loop through the Boolean values (True and False)

Since there are only two values, you can just feed a list comprehension with [True,False].

...

Last but not least, in the "loop" function above, assuming that there is a way to repeatedly call the "and" function, how could you intersperse "printStr"s between the "and" calls?

I would't - keep the the calculation and the output separate instead.

-k

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