On 10/9/07, Jonathan Cast < jonathanccast@fastmail.fm> wrote:

On Tue, 2007-10-09 at 13:07 -0700, Don Stewart wrote:
> jonathanccast:
> > I just noticed that pi doesn't have a default definition in the standard
> > prelude, according to the Haddock docs.  Why is this?
>
>     $ ghci
>     Prelude> :t pi
>     pi :: (Floating a) => a
>
>     Prelude> pi
>     3.141592653589793
>
> It's in the Floating class.

Yes.  But it doesn't have a default implementation.  That strikes me as
odd, considering the mathematical and actual correctness of

class Floating sigma where
   pi = acos (-1)
   ...

jcc

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