[Haskell] A riddle...
Vo Minh Thu
noteed at gmail.com
Mon Jul 16 17:33:48 CEST 2012
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.
2012/7/16 Andreas Abel <andreas.abel at ifi.lmu.de>:
> 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?
> Andreas Abel <>< Du bist der geliebte Mensch.
> Theoretical Computer Science, University of Munich
> Oettingenstr. 67, D-80538 Munich, GERMANY
> andreas.abel at ifi.lmu.de
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