Numeric read seems too strict
David Feuer
david.feuer at gmail.com
Sun Oct 2 04:26:10 UTC 2016
Yeah, that. With a paren count and an accumulator and for fractional
numbers some care around the decimal point or slash, we can look at each
digit just once. Fast/lazy failure would be a pleasant side effect of
running a numbers-only process from top to bottom. Yes, Read is supposed to
read things that look like Haskell expressions, but it's really not a
Haskell parser and pretending it is only hurts.
On Oct 2, 2016 12:07 AM, "Ivan Lazar Miljenovic" <ivan.miljenovic at gmail.com>
wrote:
> On 2 October 2016 at 14:34, David Feuer <david.feuer at gmail.com> wrote:
> > Instead of scanning first (in lexing) to find the end of the number and
> then
> > scanning the string again to calculate the number, start to calculate
> once
> > the first digit appears.
>
> As in multiply the current sum by 10 before adding each new digit?
>
> >
> >
> > On Oct 1, 2016 10:07 PM, "wren romano" <winterkoninkje at gmail.com> wrote:
> >>
> >> On Mon, Sep 12, 2016 at 11:03 AM, David Feuer <david.feuer at gmail.com>
> >> wrote:
> >> > By the way, I believe we should be able to read numbers more
> efficiently
> >> > by
> >> > parsing them directly instead of lexing first. We have to deal with
> >> > parentheses, white space, and signs uniformly for all number types.
> Then
> >> > specialized foldl'-style code *should* be able to parse integral and
> >> > fractional numbers faster than any lex-first scheme.
> >>
> >> I follow the part about parentheses and negations, but I'm not sure I
> >> get the rest of what you mean. E.g., I'm not sure how any parser could
> >> be faster than what bytestring-lexing does for Fractional and Integral
> >> types (ignoring the unoptimized hex and octal functions). What am I
> >> missing?
> >>
> >> --
> >> Live well,
> >> ~wren
> >
> >
> > _______________________________________________
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> > Libraries at haskell.org
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> >
>
>
>
> --
> Ivan Lazar Miljenovic
> Ivan.Miljenovic at gmail.com
> http://IvanMiljenovic.wordpress.com
>
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