[Haskell-cafe] Re: pi

[Jonathan Cast]

On Thu, 2007-10-11 at 07:57 +0000, Aaron Denney wrote:
> On 2007-10-11, Jonathan Cast <jonathanccast at fastmail.fm> wrote:
> > Yes.  I am very eager to criticize your wording.  To wit, I'm still
> > failing to understand what your position is.  Is it fair to say that
> > your answer to my question, why pi has no default implementation, is `in
> > fact, pi shouldn't be a method of Floating anyway'?
> 
> That was how I was reading him.
> 
> > Btw: I am arguing that I (still) don't understand why the line
> >
> > pi = acos (-1)
> >
> > or something like it doesn't appear at an appropriate point in the
> > Standard Prelude, given that the line
> >
> > pi :: a
> >
> > appears nearby said point.  I am eager to be enlightened.  But I haven't
> > been, yet.
> 
> You would have to ask the committee.  But I think it's a bad idea to
> have such a default (or 4 * atan 1, or ...) because of calculational
> issues.  It's not a useful default, except for toy uses.  Yeah, it works
> "fine" for float and double on hardware with FPUs.  But I want to be
> told that I haven't implemented it, rather than it getting a really
> awful default.  Most of the defaulting in other classes are minor
> wrappers, such as converting between (<=) and compare, not actual
> algorithmic implementations, which can pull in strongly less efficient
> implementations.

Fair enough.

jcc