World: r3wp

If you don't know what pattern the data is .. you can't parse it 
with anything.

parse "This is Apple . This is Windows ! This is Linux . This is 
Amiga ." [ some [ "This is" copy IT (print IT) to [ "." | "!" ] ]

The pattern is known ... the scentence starts with this is and can 
end with . or ! but they can come in any order .. if you try to parse 
with "." first you will get 
---- ops some errors upthere  .. just a sec

>> parse "This is Apple . This is Windows ! This is Linux . This 
is Amiga ." [
 some [ thru "This is" copy IT [to "." | to "!" ] (print IT) ]]
 Apple
 Windows ! This is Linux
 Amiga

this is the common to all problems where that I am describing .. 
if I had  > to [ "." | "!" ] and parse would find both and go to 
the one that is closer it would be solved.

charset [ #"!" #"." ]

ok , you again found a solution to my specific problem :))

BUT .. what if I want to have controll there .. or if for the sake 
of example it's a more complex multicharacter difference like "<DOT>" 
"<EXCLAMATION>"

Janko, best thing to do is show us a  string you can't parse ... 
and someone will show you how to do it.

>> parse "I like Apple . I like Windows ! I like Linux . I like Amiga 
." [

[     some [ thru "I like" copy IT [to "." ( prin "so so: ") | to 
"!" (prin "v
ery much: ") ] (print IT) ]]
so so:  Apple
so so:  Windows ! I like Linux
so so:  Amiga

I don't have real example right now :) I had them few times before 
and I also asked here about them and I solved with your help somehow

I just started talking about this as a general limitation of parse 
that I meed a lot of times and I suppose Paul could of meet it when 
trying to parse CSV

janko

,"some\"thing92!","graham" I am not sure but I think here you have 
the same problem

It's not necessarily a PARSE limitation, but there are things we'd 
like PARSE to do that aren't always reasonable. :-)


TO and THRU can work very well, but that doesn't mean they'll work 
for every situation. You may have to use rules where you check for 
your target value or just SKIP, marking locations in the input as 
you go.

CSV parsing is an issue, because REBOL handles some inputs well, 
but fails for what may be a common way things are formatted. "CSV" 
isn't always as simple as it sounds.

That said, if you know the format (e.g. WRT quotes and escapes), 
it can be done with PARSE. It just may not be a one-liner.

I know parsing csv can be messy ... at least at this high level I 
don't know how to do it with escapes and commas in etc

and I know everything has limitations ... this functionality OR with 
taking the first that appears would just in practice solve me many 
cases

you have to turn off parse's default delimiters and use bitsets

(aha bitsets.. I was calling them charsets upthere)

BTW, Bolek wrote a regex engine in Rebol ...

http://www.mail-archive.com/[rebol-bounce-:-rebol-:-com]/msg01983.html

Janko: the only problem is, that you cannot use:

C: [to [A | B]]

, where A and B are "general rules", but you can always write:

C: [here: [A | B] :here | skip C]

, which would do what you want

Just would like to remember that there is something like R3 where:

>> parse "I like Apple . I like Windows ! I like Linux . I like Amiga 
." [any ["I like " copy x to [" ." | " !"] (probe x) to "I like "]]
Apple
Windows
Linux
Amiga

And Janko... if you don't use charsets at all, I think you should 
give it a try. It's not so difficult. I think that if I can write 
parser to colorize PHP code, than you can parse everything.

Ladislav, thanks.. I didn't know you could set the position back 
with :here , that is interesting and probably expands what you can 
do with parse a lot.

Oldes if that is in R3 >> copy x to [" ." | " !"]  << this is exactly 
as I was proposing above :) , very nice!


I know I have to .. I haven't really needed them yet I guess, I solved 
some things less elegantly in other ways without them. I intend to 
take the plunge next time I need them.

yes, you are right .. if you can write partser for php then you can 
make anything with it. I always supposed parse with charsets is like 
low level step by one char in a looop and call "events" and change 
states , with which you can parse anything from xml to languages 
.. well but parse with charsets is still much more elegant

but it is a level less simple and nice to use than simple parse modes 
that's why the simple ones should be powerfull *if possible* too 
- you can't get a newbie impressed with charset parsing because he 
won't understand it probably.

Just to complete the list of possible equivalents to the

    C: [to [A | B]]

rule, here is a way how to do it in Rebol3 parse:

    C: [while [and [A | B] break | skip | reject]]


you can find other equivalent idioms at http://en.wikibooks.org/wiki/REBOL_Programming/Language_Features/Parse#Parse_idioms

I didn't know you could set the position back with :here

 - you can set the position back even without :here, the choice operator 
 is sufficient for you to be able to do that, see the above idioms 
 as an example

It looks, that I could have used:

    C: [while [and [A | B] accept | skip | reject]]

Janko, charset is short for make bitset! so you can call them bitsets 
or charsets :)

Ladislav, what 'choice operator?

|

Help!  Still struggling to understand parse.  How could I replace 
any and all SINGLE occurrences of  the single-quote character anywhere 
in a string (beginning, middle or end) with TWO single-quotes?  But 
if there are already TWO single-quotes together, I want to leave 
them alone.

TIA for any and all help for a newbie!

easy, actually.  you match double quotes first then fallback to single 
quotes, adding a new one and skiping one char... 

give me a minute I should get something working...

R2?

yes, View 2.7.6 under Windows XP

>> parse/all str [ any [thru {"} [{"} | p: (insert p {"} skip) ]]]
something like this (not tested)

i think i misunderstood something, replace {"} by {'} maybe

>> str: {1 ''2 '3 4 ' '5 ''6 '7 8 9 '0'}

>> parse/all str [some [{''} | [{'} here: (insert here {'}) skip] 
| skip]]
>> print str
== {1 ''2 ''3 4 '' ''5 ''6 ''7 8 9 ''0''}

note all ticks... ( ' ) are single quote chars in the above.

same as mine, except i use THRU to speed up the process

Thanks!  I'm going to have to look @ this for awhile to understand 
why you even need to worry about the double-quote character.  Much 
to learn....

Thanks Maxim and Steeve for the prompt replies!

print it out in the rebol console... you will see that my exampe 
doesn't nave any double quote characters.. they just look like so 
in altme's font  ;-)

corrected version with thru:

>> parse/all str [ any [thru {'} [{'} | p: (insert p {'} ) skip ]]]

Ah!  when you said "...you match double quotes first then fallback 
to single quotes, ..." I was thinking double-quote character, not 
double single-quotes.  Need more coffee...

Thanks very much!

( I can see that being misleading when read hehehe :-)

Just curious, I tested both versions and Steeve's version is about 
2times faster than Maxim's :)