On 16:20 Thu 04 Mar , Daniel Fischer wrote:
Yes, without rules, realToFrac = fromRational . toRational.
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I think one would have to add {-# RULES #-} pragmas to Graphics.Rendering.OpenGL.Raw.Core31.TypesInternal, along the lines of
{-# RULES "realToFrac/CDouble->GLdouble" realToFrac x = GLdouble x "realToFrac/GLdouble -> CDouble" realToFrac (GLdouble x) = x #-}
These rules are, alas, *not* equivalent to fromRational . toRational. Unfortunately, realToFrac is quite broken with respect to floating point conversions, because fromRational . toRational is entirely the wrong thing to do. I've tried to start some discussion on the haskell-prime mailing list about fixing this wart. In the interim, the OpenGL package could probably provide its own CDouble<=>GLDouble conversions, but sadly the only way to "correctly" perform Double<=>CDouble is unsafeCoerce. -- Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)