World: r3wp

where the 'slash' can be in the paren as well (so I cannot use just 
parse str "/")

here is a full script  :-) 


rebol []

paren-start: charset "("
paren-end: charset ")"
parens: union paren-start paren-end

separator: charset [#"/" #"."]
label: complement union separator parens

content: complement parens
blk: copy []

str: {some.string/(a + 1 / 2 (b.a * c()))/end}

expression: [paren-start  any [content | expression] paren-end]

parse/all str [some [ separator | here: some [label] there:  (append 
blk copy/part here there) | here:   expression there: (append blk 
copy/part here there)]]


probe blk


ask "..."

Thank you Maxim:-]

IIRC someone created an inference motor using parse, unfortunalty 
i'm unable to recover the sources, someone can help me ?

What do you mean?  Is it encapped?

sorry ? what do you  mean by encapied ? IIRC it was running  using 
parse dialect

*encapped

You saw it before, now you can't find it, and wish for someone else 
to help.

What did it do ?

Encapping is using the rebol SDK to "compile" rebol sources into 
an executable (from which it is obviously difficult to extract the 
sources).

the goal was to resolve rules (like described with prolog)

it's the use of an inference motor, usally

*usually

This one?

http://www.rebol.org/cgi-bin/cgiwrap/rebol/view-script.r?script=prolog.r

not this one

but the same goal

do you remember the author ?

no sorry

i'ts verry old

rebol.org was not created yet

i mean

But you were not around at this time, were you ?

i was

i'm using Rebol since 6 years at least

i made pauses

aha ok

I made a pause during which I raised sheep in the French Alps

and other ecological activities

and reality kicked in?

the reality ?, i'm just a nerd, i must admit this weakness, i can't 
leave without technology

*can't live

hehe not enough buttons on a sheep I guess  ;-)

I tested sincerely, but to live without technology it is like living 
with the Middle Ages, one passes the three quarters of his time to 
produce his food and to make provisions for the winter .

that's why the stoneage was not known for it's artistic achievements

I've never heard of such a script, Steeve.

It does not seem to be on REBOLtech (a forerunner to REBOL.org). 
You could try some more detailed searches than I did if you want 
to look further
http://www.reboltech.com/library/scripts/
****

Sadly, a lot of good stuff gets published on personal websites, and 
when the enthusiasm for REBOL wanes, or the site is taken offline 
for some reason, the scripts are lost to the wider community.

Steeve, you can have a look at the scripts archive

http://www.rebol.org/cgi-bin/cgiwrap/rebol/ml-display-thread.r?m=rmlYCHQ

I forget whether it's possible to move backwards in the block I'm 
parsing?

yes, it is

... how? :-)

>> firsttime?: true parse [1 2 3 4 5][any [set v integer! p: (prin 
v if all [firsttime? v = 4][p: skip p -2 firsttime?: false]) :p]]
1234345== true

I'm not sure I get it. how does parse know how to deal with 'p?

p:  gets current parse position
:p  sets new position

but it must be in documentation somewhere

it does, but I still don't see it. does parse read the block at the 
end of the 'any block?

You can use it not just inside any block

but don't know any example why to use it without some rule like 'any

>> parse [1 2 3 4 5] [any [p: (probe p) skip]]
[1 2 3 4 5]
[2 3 4 5]
[3 4 5]
[4 5]
[5]
[]

gave up. two-pass is easier :-)

Here is Oldes example padded with comments:

firsttime?: true 
parse [1 2 3 4 5][
	any [
		set v integer! 
		p:   ; <-- set P to the current parse position.

       ; (This is the input series with the series index at the current 
       position.)
		
		(
			; Here inside the paren is normal rebol code 
			
			prin v 
			if all [firsttime? v = 4][

    p: skip p -2   ; <-- move the index of the series referred to by 
    P
				firsttime?: false
			]
		) 
		
		:p   ; <-- set the current parse position to P
	]
]