On 16/12/2010, at 6:22 PM, john skaller wrote:
>
> // alternate encoding
> var digit = #(charset "9" );
> var digits = #(digit+);
> var letter = #(charset "x");
> var us = #("_");
> var id = #( (us|letter)(letter|digit|us)*);
I have now fixed this to use "regexp" instead of "#". So the competition is now
on
to design a nice syntax!
For example, instead of
regex (charset "0123456789")
we might want
regex ( ["0123456789"] )
since that is closer to the traditional notation. The constraints here are: it
has to fit in
to the existing grammar and lexicology, so we will NOT allow this:
regex ( [0123456789] )
without some very serious thinking, because it requires a completely new lexing
rule just for
charsets (any sequence of characters other than ], but - has special meaning as
does ^ at the start).
The existing notation is:
expr = regex ( re )
re = charset string-literal // string considered as character set
re = string // match the string literally
re = identifier // name of a Felix variable of regex type
re = a | b | c | ... // alternatives
re = a b c d // sequence
re = ( r ) // non-capturing group
re = group (r) // capturing group
re = perl (string-expr) // a string considered as a Perl regexp
re = felix ( re ) // a felix expression returning a regex
re = r* // 0-infinte repeat
re = r+ // 1-infinite repeat
re= r? // optional, 0-1 repeat
string = render re // make a Perl encoded regex string from a
regex
Google Re2 supports a lot more, such as named charsets, words,
and some other stuff (NOT backreferences), numbered repeats
r {min,max}
You should note again: this stuff generates regexps dynamically.
It is miles better than any other way, because you can get all the grouping
and quoting right because you simply don't have to do it.
--
john skaller
skal...@users.sourceforge.net
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