Decimal & Ratio (Was: Block-I/O in Haskell)
Krasimir Angelov
ka2_mail at yahoo.com
Fri Oct 15 03:55:39 EDT 2004
The usage of ratio is also too slow. The
disadvantage of Double and Float is that often the
result of computation isn't correct. For example if we
have a lot of small values then its sum will not be
precise. This is very important in financial
applications. For such reason in SQL is defined
decimal data type. In MS COM there are DECIMAL and in
.NET there are decimal types. I would like to see
Decimal type in Haskell too. In the Mono project there
is a free and portable implementation of decimals
which we can adopt in Haskell. The Ratio type is
simply too expensive in many cases. Of course to adopt
Decimal properly in Haskell we need to have support in
the compiler too.
Cheers,
Krasimir
--- Tomasz Zielonka <t.zielonka at students.mimuw.edu.pl>
wrote:
> On Fri, Oct 15, 2004 at 01:15:16AM -0400, David
> Menendez wrote:
> > Tomasz Zielonka writes:
> > > Hmmm, that's right. Perhaps it would be best to
> use some fixed-point
> > > type with unbounded integral part, like those
> used for representing
> > > currency, but not necessarily decimal.
> >
> > I'd go with ratios. Haskell has a built-in type,
> and they can give you
> > as many digits of precision as you need--unless
> you're dealing with an
> > irrational timeout value.
>
> Unfortunately, they have the unpleasant tendency
> that after many
> operations even if the absolute value is small, the
> two integers that
> constitute the ratio can be very big. That's why (I
> think) it's not that
> good idea to solve linear equation systems using
> unbounded ratios.
>
> Why not use typeclasses and let the user decide?
>
> Best regards,
> Tom
>
> --
> .signature: Too many levels of symbolic links
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