[REBOL] Re: Parse and and recursion local variables?
From: volker:nitsch:gmai:l at: 19-Mar-2007 12:46
Am Sonntag, den 18.03.2007, 17:33 -0500 schrieb Maxim Olivier-Adlhoch:
> thru [a | b] is not only a problem in learning... its a valid extension
> cause it can simply many complex rules, by not having to explicitely
> implement all possible variations as rules.
>
> but I am almost sure that it would lead to regexp like slowdown in some
> rules ' :-/
>
> why are charsets clumsy?
>
> -MAx
>
any [ thru [ a | b ] ]
is similar to as
any[ a | b | skip ]
and
thru[ a | b ]
to
some[ a break | b break | skip]
So its there. If you know how. As with stacks and parse-recursion ;)
Slowdown yes :)
charsets are clumsy because they are defined somewhere and not in the
rule. And they are look ugly, this #"c".
digits: charset[ #0" - #"9" ]
rule: [ some[ digit ] ]
Thats natural for BNF-academics. But
rule: [ some [ 0 - 9 ] ]
would be much nicer.
