Re: Random Color
On Thu, 21 Nov 2002, Mike T. Machenry wrote:
> This program yeilds:
> Fail: toEnum{Color}: tag (4) is outside of enumeration's range (0,3)
> in ghc... any ideas why?
>
> -mike
Hmm. The program works fine for me, using GHC 5.04.1 or Hugs of Oct 2002.
Dean
> On Thu, Nov 21, 2002 at 10:07:12AM -0500, Dean Herington wrote:
> > "Mike T. Machenry" wrote:
> >
> > > Andrew and list,
> > >
> > > I am a beginer. I really don't know what I would do if I derived
> > > Color from Enum. You say I could create elements that way. Is there
> > > some simple example someone could post to the list? Thank you for
> > > your help.
> >
> > Here's one way to generate random values from an enumerable set:
> >
> > import Random
> >
> > randomR_Enum :: (Enum a, RandomGen g) => (a, a) -> g -> (a, g)
> > randomR_Enum (lo, hi) gen = (toEnum val, gen')
> > where (val, gen') = randomR (fromEnum lo, fromEnum hi) gen
> >
> > random_EnumBounded :: (Enum a, Bounded a, RandomGen g) => g -> (a, g)
> > random_EnumBounded = randomR_Enum (minBound, maxBound)
> >
> > data Color = Blue | Red | Green deriving (Show, Enum, Bounded)
> > instance Random Color where
> > randomR = randomR_Enum
> > random = random_EnumBounded
> >
> > main = do stdGen <- getStdGen
> > print (take 10 (randoms stdGen :: [Color]))
> >
> >
> > Dean
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Re: Random Color
This program yeilds:
Fail: toEnum{Color}: tag (4) is outside of enumeration's range (0,3)
in ghc... any ideas why?
-mike
On Thu, Nov 21, 2002 at 10:07:12AM -0500, Dean Herington wrote:
> "Mike T. Machenry" wrote:
>
> > Andrew and list,
> >
> > I am a beginer. I really don't know what I would do if I derived
> > Color from Enum. You say I could create elements that way. Is there
> > some simple example someone could post to the list? Thank you for
> > your help.
>
> Here's one way to generate random values from an enumerable set:
>
> import Random
>
> randomR_Enum :: (Enum a, RandomGen g) => (a, a) -> g -> (a, g)
> randomR_Enum (lo, hi) gen = (toEnum val, gen')
> where (val, gen') = randomR (fromEnum lo, fromEnum hi) gen
>
> random_EnumBounded :: (Enum a, Bounded a, RandomGen g) => g -> (a, g)
> random_EnumBounded = randomR_Enum (minBound, maxBound)
>
> data Color = Blue | Red | Green deriving (Show, Enum, Bounded)
> instance Random Color where
> randomR = randomR_Enum
> random = random_EnumBounded
>
> main = do stdGen <- getStdGen
> print (take 10 (randoms stdGen :: [Color]))
>
>
> Dean
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Re: Random Color
"Mike T. Machenry" wrote: > Andrew and list, > > I am a beginer. I really don't know what I would do if I derived > Color from Enum. You say I could create elements that way. Is there > some simple example someone could post to the list? Thank you for > your help. Here's one way to generate random values from an enumerable set: import Random randomR_Enum :: (Enum a, RandomGen g) => (a, a) -> g -> (a, g) randomR_Enum (lo, hi) gen = (toEnum val, gen') where (val, gen') = randomR (fromEnum lo, fromEnum hi) gen random_EnumBounded :: (Enum a, Bounded a, RandomGen g) => g -> (a, g) random_EnumBounded = randomR_Enum (minBound, maxBound) data Color = Blue | Red | Green deriving (Show, Enum, Bounded) instance Random Color where randomR = randomR_Enum random = random_EnumBounded main = do stdGen <- getStdGen print (take 10 (randoms stdGen :: [Color])) Dean ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Random Color
Andrew and list, I am a beginer. I really don't know what I would do if I derived Color from Enum. You say I could create elements that way. Is there some simple example someone could post to the list? Thank you for your help. -mike On Thu, Nov 21, 2002 at 01:55:55PM +1100, Andrew J Bromage wrote: > G'day all. > > On Wed, Nov 20, 2002 at 08:44:36PM -0500, Mike T. Machenry wrote: > > > I am trying to construct an infinate list of pairs of random colors. > > I am hung up on getting a random color. I have: > > > > data Color = Blue | Red | Green deriving (Eq, Ord, Show) > > > > am I supposed to instantiate a Random class instance from color? > > You could derive instances of Enum (and possibly also Bounded) and > create random elements that way. > > Cheers, > Andrew Bromage ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Random Color
G'day all. On Wed, Nov 20, 2002 at 08:44:36PM -0500, Mike T. Machenry wrote: > I am trying to construct an infinate list of pairs of random colors. > I am hung up on getting a random color. I have: > > data Color = Blue | Red | Green deriving (Eq, Ord, Show) > > am I supposed to instantiate a Random class instance from color? You could derive instances of Enum (and possibly also Bounded) and create random elements that way. Cheers, Andrew Bromage ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
