Red parse with break

Question

my parse code with break doesn't work, I shouldn't get last div block in text:

src: { <div class="main"> <div> test </div> <div> test2 </div> <div> test3 </div> </div> <div class="test"> </div> } rules: [ (div-count: 0) some [ to "<div" (div-count: div-count + 1) [if (div-count = 1) mark1:] | thru "</div>" (div-count: div-count - 1) [if (div-count = 0) mark2: break] ] text: copy/part mark1 mark2 ] parse src rules print text

Expected result I want is:

 { <div class="main"> <div> test </div> <div> test2 </div> <div> test3 </div> </div> }

sqlab · Accepted Answer · 2018-05-01 09:06:23Z

An answer for Red and Rebol could look like this

rules: [ (div-count: 0 clear rules/3/8 ) some [ mark: "<div" (if equal? 1 div-count: div-count + 1 [ mark1: mark ] ) | "</div>" mark2: ( if equal? 0 div-count: div-count - 1 [ text: copy/part mark1 mark2 insert rules/3/8 [to end] ] ) [] | skip ] ]

One of the problems with your rules are that you use to and | (meaning or) thru, so that most closing </div> s would be skipped. The first match <div is satisfied and on to the next opening<div without comparing the following sub rules. But the cursor is not advancing, the next <div is still the same. Probably Red discovers the endless loop (no advancing) and interrupts it.

I use dynamically modified rules instead of break, as break breaks out of (sub) rules in Rebol, but does not stop the whole parsing process as you can see here.

 >> parse "aaa" [(n: 0)some ["a" [break] (ask form n: n + 1) ]] 1 2 3 == true

That's different to Red, where it interupts parse.

>> parse "aaa" [(n: 0)some ["a" [break] (ask form n: n + 1) ]] 1 == false

So a simple solution suitable for Red, not for Rebol can look like that

rules: [ (div-count: 0) some [ mark: "<div" (if equal? 1 div-count: div-count + 1 [mark1: mark]) | "</div>" mark2: if (equal? 0 div-count: div-count - 1 ) [(print text: copy/part mark1 mark2 ) break] | skip ] ]

Could you explain why you do need clear rules/3/8 : do you change rules dynamically ?
still why conditional break doesn't work: is my program buggy or red buggy ?
Yes, I change the rules dynamically. [] does nothing. It is just a place holder, that gets filled. Your program seems to be a endless loop that gets discovered by Red and stopped as the cursor is not advancing

DocKimbel · Accepted Answer · 2018-05-06 07:42:00Z

Here is an alternative parametrized way to parse it:

div: ["<div" 4 skip some ["</div>" break | div | skip] | skip] div-rule: [to "<div" div] n: 1 parse src compose [(n - 1) div-rule copy text div-rule to end]

With n: 1, it will extract the first root <div>, with n: 2, the second one, and so one. It should be possible to also parametrize the nested rules to extract arbitrary <div> sections.

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