[Haskell] A riddle...

[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 <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?
>
> Cheers,
> Andreas
>
> --
> 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
> http://www2.tcs.ifi.lmu.de/~abel/
>
>
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