World: r3wp

true functional unfolding  :-)

the Rebol programming wikibook contains a bunch of such idioms

and THRU multi is even simpler:

    a: [thru b]

is equivalent to

    a: [b | skip a]

yep... all hard to understand and code in real life.  which is why 
I say that the new keywords, just make it easier to parse stuff. 
 They aren't hacks or tricks anymore, they are supported directly 
by the parse dialect.


its like the stack handling... its just going to be MUCH simpler 
so use push, than tinker with your own stack.

or rather 'USE ... sorry.

I'm not saying STAY isn't useful, just that it is lower priority 
than AND because it's use is more limited.

you see the thru multi you show... is excessively hard to "see", 
even I look at it and have to wrap my brain against it, and its really 
not "obvious"

I like having STAY though, since I am one of the advanced parse users 
that would find use for it, like Maxim and Carl :)

we will see...

A

as shown above, it is superfluous; the a: [b fail |] rule is exactly 
as simple as a: [stay b]

All of the new additions are superfluous, Ladislav. They were added 
to make our lives easier, not to enable stuff we couldn't do before.

I'm  looking at this.....    a: [b fail |]  and its totally obscure 
... I don't see it at all, I can study and eventually "understand" 
it, but within a 1000 line parse rule... <eek>. 

the way I see STAY is: [pos: b :pos]

(speaking as a general user... not myself specifically)

Sorry, that's still AND. STAY is [pos: opt b :pos].

well, I do not think, that e.g. NOT is superfluous, since it substantially 
simplifies the expression. This is not true for STAY.

The fact is that all of these were added to make our lives easier. 
Now I don't think STAY is worth the effort to implement it, but given 
that Carl *already has* implemented it, it it worth removing? This 
is regardless of the merits of AND, which are unquestioned.

NOT is very important, especially because charset can't be complemented 
in R3 (Actually they can, but it's a monstrous thing to add all the 
possible chars in a bitset, just to skip someones)

I agree that if we were to dump all of the enhancements but one, 
NOT is the one I would choose :)

We could fix charsets too (add a complemented bit), and that would 
help too.

would be useful for FIND

unless Carl implements the find/not refinement

I agree that if we were to dump all of the enhancements but one, 
NOT is the one I would choose :)
 - I guess, that it is my favourite too

Carl *suggested* the find/not option :)

'NOT  and the 'TO/'THRU multi.  its just soooo much simpler to slice 
and dice text using it, which is a large percentage of what parse 
is used for.


I remember Carl's historical reason that it made us lazy... hehehe... 
his CR.LF stripping example shows that he is quite lazy himself  
;-)

TO/THRU multi is not so important in text parsing because we can 
use charsets

I am just curious, whether Carl intends to implement the full TO/THRU, 
acting on any subrule

it's working now in a84

It is badluck, that recursive rules are not useful in fact, since 
the stack is too small :-(

There are likely to be limits. I'm a bit shocked that he was able 
to push it as far as he did :)

steeve, it is... you don't have to build a grammar, just find a set 
of words...

I also remember that Carl feared it would lead to people building 
RE-like slow parsers.

full TO/THRU is not implemented yet, trust me

If you say so, Ladislav, then I look forward to what is to come :)

working here

>> parse "abcd" [any [to ["c" | "b"] ?? skip]]
skip: "bcd"
skip: "cd"
== false

what do you mean by "full" implemented ?

well, but I do not know if Carl intends to implement the full TO/THRU, 
as I said...

what do I mean? the "full"

    a: [thru b]

can be defined as a "shorcut" for

    a: [b | skip a]


you can try, that this works for any rule B as far as you don't need 
to use too deep a recursion. As opposed to that, the THRU keyword 
does not accept any rule B, as documented in Carl''s blog

Right. I would just be happy if he adds the not modifier, but the 
current capabilities are moree than I was expecting.

actually, to/thru multi, is like an ANY with an embedded skip... 
I don't think there is any slowness related to it.
coudn't thru be implemented this way?

skip-rule: [skip]

thru:   [any [ ["c" (skip-rule: [fail]) |  "b" (skip-rule: [fail])] 
skip-rule]]

but the A: [b | skip A] is weird, i never do that to avoid the stack 
limit error.
this instead:
a: [
    any [
       b break
       | skip
    ]
]

the above has the advantage of not requiring stack.

you don't know break Maxim ;-)

Yes, Steeve, I used it just the recursive expression just for demonstration 
purposes (recursion can be even used to demonstrate how ANY works). 
OTOH, it is a problem to e.g. define a non-recursive rule to detect 
correctly parenthesized string containing just #"(" and #")"

So, another problem of Parse is, that recursion does not work as 
well as it should :-(

(or, as well as may be needed)

Do you mean the USE proposal, or does it suck in other ways?

just this: correct-paren: [any [#"(" correct-paren #")"]] - you can 
use it to parse strings, but just "short ones"

or, rather, just the "shallow ones"

Ah yes. For long ones you need a counter in a production.