Conditional "marking" in Rebol / Red parse

Question

Subsequent to Rebol / Red Parse html rules returns true but nothing is inserted

How to mark the end of the fist main div only (when div-count is 0 first time), not the second one, or is there a way to break out of parse conditionally to a variable value ?

        content: {<div class="main">
          <h1>
            Big TITLE
          </h1>
          <div>
            <section>
              <p>a paragraph</p>
            </section>
             <section>
              <p>a paragraph</p>
            </section>
              <section>
              <p>a paragraph</p>
            </section>
           </div>
           <div>
              <p>Blah Blah</p>
           </div>
        </div>
        <div>
          Another Div
        </div>

    <div class="main">
          <h1>
            Big TITLE
          </h1>
          <div>
            <section>
              <p>a paragraph</p>
            </section>
             <section>
              <p>a paragraph</p>
            </section>
              <section>
              <p>a paragraph</p>
            </section>
           </div>
           <div>
              <p>Blah Blah</p>
           </div>

        </div>
        <div>
          Another Div
        </div>    
        }

        rules: [
             thru <div class="main">
             (div-count: 1)
              some [
                "<div" (probe ++ div-count) skip
              |
                "</div>" mark:  ( probe -- div-count   if div-count = 0 [insert mark "closing main div"]) skip 
              |  skip
             ]
          ]
        parse/all content rules

score 3 · Accepted Answer · answered Apr 20 '18 at 14:47

It seems that you need a mix of opt and if keywords. Consider a simplified example:

count: 0
div: ['div some integer! /div]

probe parse [
    div 1 2 3 /div 
    div 4 5 6 /div
    div 7 8 9 /div
][
    some [
        div (count: count + 1) opt [if (count = 1) mark:]
    ] 
]

probe mark

Here, after each div rule match, increment of a counter happens. After that there's an optional match -- if counter is at 1, then current input position is marked, otherwise parsing continues as-is. Because this rule is optional, parsing will continue despite its success or failure.

Additionally, if you want to break out of a parsing loop (that is, some, any or while), you can use break (returns success) or reject (returns failure), again in combination with opt, if and conditional paren! expression.

sqlab · Answer 2 · 2018-04-25T11:48:27.930

2

Here a solution working in Red and Rebol using your approach plus adding some selfmodification to the rules

rules: [
    thru <div class="main">
    (div-count: 1 clear rules/5/8 )
    some [
        "<div" (probe div-count: div-count + 1) skip
        |
        "</div>" mark:  ( 
             probe div-count: div-count - 1   
             if div-count = 0 [
                 insert mark "closing main div"  append rules/5/8 [to end]  
             ]
         ) [] skip 
         |  skip
     ]
 ]

edited Apr 25 '18 at 11:48

answered Apr 24 '18 at 08:21

sqlab

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hi thanks but I don't understand what clear rules/5/8 is supposed to do ? – user310291 Apr 29 '18 at 11:56
Clearing this part of the rule (the emtpty block in the original rule) makes the rule reuseable by generating the initial rule again, if you want to use the rule more than once in a program or function. – sqlab Apr 30 '18 at 07:18

Conditional "marking" in Rebol / Red parse

2 Answers2