[Haskell-cafe] OpenGL: No instance for Random GLfloat

[L Corbijn]

Hi,

GLfloat haskell is instance of several number related typeclasses. A
function like 'fromRational' could be used to create a GLfloat from another
number that has a random instance.

L
On May 3, 2012 4:39 AM, "Mark Spezzano" <mark.spezzano at chariot.net.au>
wrote:

> Hi,
>
> I tried this but now I get another error:
>
> The data constructors of `GLfloat' are not all in scope
>       so you cannot derive an instance for it
>     In the stand-alone deriving instance for `Random GLfloat'
>
> Mark
>
> On 03/05/2012, at 10:39 AM, Patrick Palka wrote:
>
> Because GLfloat is simply a newtype wrapper for CFloat, which has a Random
> instance, I would do:
>
> {-# LANGUAGE StandaloneDeriving #-}
> {-# LANGUAGE GeneralizedNewtypeDeriving #-}
> deriving instance Random GLFloat
>
> On Wed, May 2, 2012 at 6:29 PM, Mark Spezzano <
> mark.spezzano at chariot.net.au> wrote:
>
>> Hi Haskellers,
>>
>> I'm trying to generate a random vertex in OpenGL as follows.
>>
>> genPosition :: IO (Vertex3 GLfloat)
>> genPosition = do x <- getStdRandom $ randomR (-1.6,1.6)
>>                               y <- getStdRandom $ randomR (-1.0,1.0)
>>                              return (Vertex3 x y (-1))
>>
>> Unfortunately the compiler complains about me having to implement an
>> instance of Random for  GLfloat.
>>
>> How do I do this (or avoid having to do this)?
>>
>> Cheers,
>>
>> Mark
>>
>>
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