[Haskell-cafe] fromIntegral not enough?

[Tom Ellis]

On Mon, May 13, 2013 at 11:43:41PM +0100, Tom Ellis wrote:
> On Mon, May 13, 2013 at 02:08:26PM -0800, Christopher Howard wrote:
> > instance Integral a => Coord2 (CircAppr a) where
> > 
> >   coords2 (CircAppr divns ang rad) =
> >       let dAng = 2 * pi / (fromIntegral divns) in
> >       let angles = map (* dAng) [0..divns] in
> >       undefined -- To be coded...
> 
> Your definition of "angles" forces "dAng" to be of type "a".  Then in order
> to define "dAng" as the result of a "/" there must be a "Fractional" instance for
> "a".

You probably want

    let angles = map ((* dAng) . fromInteger) [0..divns] in
    ...

instead.