Mailing List Archive: 49091 messages
  • Home
  • Script library
  • AltME Archive
  • Mailing list
  • Articles Index
  • Site search

[REBOL] Re: REBOL embedded $variables regexp/no

From: g:santilli:tiscalinet:it at: 10-Dec-2002 12:50

Hi Joel, On Monday, December 9, 2002, 8:45:19 PM, you wrote: JN> Please, everyone, before complaining about the punctuation, get over JN> it and look at the real point; that expression says (compactly) the JN> equivalent of this: [...] Joel, you are right, but also consider that if I look at it, I don't understand what it is doing. Of course, that applies to every language, but if you look at: replace/all s "tetx" "text" you can guess what it is doing even if you don't know REBOL at all. (Or, if a couple months have passed since you touched it last time, which is much more common and is the real point I wish to take.) This said, surely it would be nice to have pattern matching in REBOL. Maybe using a different notation for RegExps that is a little bit less vodoo. However, pattern matching has the disadvantage of looking a simple step, while it can be very computationally intensive; I prefer PARSE because it is very clear how complex a rule is, computationally. JN> Within the variable named "bigstring" replace all runs of JN> digits with a single pound-sign/number-sign/octothorp. Now, I don't claim this to be more readable, because you need to provide a rule to match the text that does not match the pattern rule, but I found it very easy to code it, and it looks very reusable. pattern-replace: func [string text-pattern match-pattern replacement /local result txt] [ result: make string! length? string parse/all string [ copy txt text-pattern (emit result txt) any [match-pattern (emit result replacement) copy txt text-pattern (emit result txt)] ] result ] emit: func [dest value] [if value [append dest reduce value]]
>> digits: charset "1234567890" >> chars: complement digits >> pattern-replace "Replace 5248 with a #" [any chars] [some digits] "#"
== "Replace # with a #" JN> Then think about a slightly more interesting case, such as JN> $bigstring =~ s/([A-Z][a-z]{2}) (\d{1,2}), (\d{4})/$2-$1-$3/g; If we don't care about the time it requires to do it,
>> not-rule: func [rule'] [use [rule mark] [rule: rule' copy/deep [some [mark: rule :mark break | skip]]]]
(This requires the beta for the BREAK keyword. It is possible, with a little more effort, to do the same without using BREAK.) Then:
>> string: {
{ On Dec 09, 2002 I wrote an email that talked { about modifying strings based on a match-and- { replace strategy. This was in response to { messages posted in the REBOL mailing list on { Dec 07, 2002 and Dec 08, 2002. { }
>> ucase: charset [#"A" - #"Z"] >> lcase: charset [#"a" - #"z"] >> date: [copy month [ucase 2 lcase] " " copy day 1 2 digits ", " copy year 4 digits] >> print pattern-replace string not-rule date date [day "-" month "-" year]
On 09-Dec-2002 I wrote an email that talked about modifying strings based on a match-and- replace strategy. This was in response to messages posted in the REBOL mailing list on 07-Dec-2002 and 08-Dec-2002. (You might argue that NOT-RULE is tricky; I agree, however once you have included it in REBOL/Core you just need to use it.) With a little more effort, one could write a faster rule for matching the text that is not a date. JN> Again, I think the real question is how much code the REBOL programmer JN> has to write to get the equivalent transformation. I don't think that it is too much. Of course, you could use shorter words etc. in the above code to reduce the keystrokes. :-) JN> As PARSE is an all-or-nothing affair, I believe that it currently JN> requires the programmer to work harder to do these kinds of tasks. Matching a pattern and defining a grammar are two different things, of course. However, I am convinced that grammars are much more general and useful than patterns. IMHO, Gabriele. -- Gabriele Santilli <[g--santilli--tiscalinet--it]> -- REBOL Programmer Amigan -- AGI L'Aquila -- REB: