[Haskell-cafe] opengl type confusion

[L Corbijn]

On Sun, Jun 16, 2013 at 10:42 PM, <briand at aracnet.com> wrote:

> On Sun, 16 Jun 2013 16:15:25 -0400
> Brandon Allbery <allbery.b at gmail.com> wrote:
>
> > On Sun, Jun 16, 2013 at 4:03 PM, <briand at aracnet.com> wrote:
> >
> > > Changing the declaration to GLdouble -> GLdouble -> GLdouble -> IO()
> and
> > > using
> > > (0.0::GLdouble) fixes it, and I'm not clear on why it's not automagic.
> > >  There are many times I see the
> >
> >
> > Haskell never "automagic"s types in that context; if it expects GLdouble,
> > it expects GLdouble. Pretending it's Double will not work. It "would" in
> > the specific case that GLdouble were actually a type synonym for Double;
> > however, for performance reasons it is not. Haskell Double is not
> directly
> > usable from the C-based API used by OpenGL, so GLdouble is a type synonym
> > for CDouble which is.
> >
> > compiler doing type conversion an numerican arguments although sometimes
> > > the occasional fracSomethingIntegralorOther is required.
> > >
> >
> > I presume the reason the type specification for numeric literals is
> because
> > there is no defaulting (and probably can't be without introducing other
> > strange type issues) for GLdouble.
> >
>
> What I was thinking about, using a very poor choice of words, was this :
>
>
> *Main> let a = 1
> *Main> :t a
> a :: Integer
> *Main> let a = 1::Double
> *Main> a
> 1.0
> *Main> :t a
> a :: Double
> *Main>
>
> so normally 1 would be interpreted as an int, but if I declare 'a' a
> Double then it gets "promoted" to a Double without me having to call a
> conversion routine explicitly.
>
> That seems automagic to me.
>
> (0.0::GLdouble) works to make the compiler happy.  So it appears to be
> taking care of the conversion automagically.
>
> So maybe a better question, I hope, is:
>
> How can I simply declare 0.0 to be (0.0::GLdouble) and have the functional
> call work.  Doesn't a conversion have to be happening, i.e. shouldn't I
> really have to do (realToFrac 0.0) ?
>
> Brian
>
>
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