[Haskell-cafe] Fortran mixed mode arithmetic expressions ->
Haskell
Ross Mellgren
rmm-haskell at z.odi.ac
Mon Oct 26 15:21:49 EDT 2009
http://www.haskell.org/onlinereport/basic.html
6.3 Standard Haskell Classes
-Ross
On Oct 26, 2009, at 3:13 PM, michael rice wrote:
> Got it. No doubt some of this figures into why I was beaten bloody
> by ghci last night. Is there a number "tree" somewhere that shows
> the heirarchy?
>
> Michael
>
> --- On Mon, 10/26/09, Daniel Fischer <daniel.is.fischer at web.de> wrote:
>
> From: Daniel Fischer <daniel.is.fischer at web.de>
> Subject: Re: [Haskell-cafe] Fortran mixed mode arithmetic
> expressions -> Haskell
> To: "michael rice" <nowgate at yahoo.com>, haskell-cafe at haskell.org
> Date: Monday, October 26, 2009, 1:09 PM
>
> Am Monday 26 October 2009 17:24:46 schrieben Sie:
> > Being new to Haskell, I take it (^) and (^^) would be the preferred
> > exponential "operator." When (how,where,why) would one use (**)?
>
> The beasts have different types and are for different things:
> Prelude> :i (^)
> (^) :: (Num a, Integral b) => a -> b -> a -- Defined in GHC.Real
> infixr 8 ^
>
> This one raises any number to a nonnegative integral power.
> A typical implementation would be power by repeated squaring.
>
> Prelude> :i (^^)
> (^^) :: (Fractional a, Integral b) => a -> b -> a
> -- Defined in GHC.Real
> infixr 8 ^^
>
> This one allows also negative powers, so the type of base must allow
> inversion, hence it
> must belong to Fractional. The exponent must still be an integer,
> you can't use this for
> n-th roots or similar.
> A typical implementation would be power by repeated squaring,
> followed by (1/) if the
> exponent is negative.
>
> Prelude> :i (**)
> class (Fractional a) => Floating a where
> ...
> (**) :: a -> a -> a
> ...
> -- Defined in GHC.Float
> infixr 8 **
>
> This one raises a floating point number to an arbitrary power, so
> you can use it for n-th
> roots.
> A typical implementation would be
> b ** e = exp (e*log b).
>
>
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