[Haskell-cafe] pi

[Jonathan Cast]

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