Re: [Haskell-cafe] [Haskell] A riddle...

Oh the mailing list was haskell@ instead of café. Sorry. (Now cc'ing café.) Andreas, please post this kind of mail to the haskell-cafe instead of the haskell mailing list. 2012/7/16 Vo Minh Thu :

It seems like the infered type (and thus bounds) is different when you force the result to be a Color or not. Just give explicit type signatures and conversion functions.

Cheers, Thu

2012/7/16 Andreas Abel :

...

Today a student came to me with a piece of code that worked it executed by itself, but produced different result in the context of his larger problem. We cut down the example to the following:

...

import Graphics.UI.Gtk

-- should produce [(26471,0,65535),... rgbliste = (map (\ i -> let rb = 5 * (mod (mod 181935629 (4534+i)) 100)-250+128 in let gb = 5 * (mod (mod 128872693 (5148+i)) 100)-250+128 in let bb = 5 * (mod (mod 140302469 (7578+i)) 100)-250+128 in let r = min 255 $ max 0 rb in let g = min 255 $ max 0 gb in let b = min 255 $ max 0 bb in (r*257,g*257,b*257)) [0..])

--farbliste = map (\ (r,g,b) -> Color r g b) rgbliste

main :: IO () main = do print $ head rgbliste

If you run it, it prints (26471,0,65535). If you uncomment the def. of farbliste, it prints (44461,65535,65535).

I was surprised. What is going on?

Cheers, Andreas

-- Andreas Abel <>< Du bist der geliebte Mensch.

Theoretical Computer Science, University of Munich Oettingenstr. 67, D-80538 Munich, GERMANY

andreas.abel@ifi.lmu.de http://www2.tcs.ifi.lmu.de/~abel/

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