REx EBNF for a parsing problem presented by Martynas Jusevičius on the xml.com slack

invocation.sh

# Go to https://bottlecaps.de/rex/ and use this command line on nested-parentheses.ebnf: -xslt -main -tree -ll 3 -backtrack
# Assumption: A Saxon front-end script called 'saxon' is on the path
saxon -o:out.xml -it:main -xsl:nested-parentheses.xslt input='{(((40 40, 20 45, 45 30, 40 40)), ((20 35, 10 30, 10 10, 30 5, 45 20, 20 35), (30 20, 20 15, 20 25, 30 20)))}' '!indent=yes'
# Looking at the main template of the generated XSLT, you need to surround the input string with curly braces; otherweise it will be interpreted as a file name

nested-parentheses.ebnf

nested_parentheses ::= '(' ( nested_parentheses (',' S* nested_parentheses)* | tuple_sequence ) ')' S*
tuple_sequence ::= ( tuple (',' S* tuple)* )
tuple ::= digits S+ digits

<?TOKENS?>
digits      ::= [0-9]+
S        ::= [ #x0009#x000D#x000A#x000C]+

out.xml

<?xml version="1.0" encoding="UTF-8"?>
<nested_parentheses>
   <TOKEN>(</TOKEN>
   <nested_parentheses>
      <TOKEN>(</TOKEN>
      <nested_parentheses>
         <TOKEN>(</TOKEN>
         <tuple_sequence>
            <tuple>
               <digits>40</digits>
               <S> </S>
               <digits>40</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>20</digits>
               <S> </S>
               <digits>45</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>45</digits>
               <S> </S>
               <digits>30</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>40</digits>
               <S> </S>
               <digits>40</digits>
            </tuple>
         </tuple_sequence>
         <TOKEN>)</TOKEN>
      </nested_parentheses>
      <TOKEN>)</TOKEN>
   </nested_parentheses>
   <TOKEN>,</TOKEN>
   <S> </S>
   <nested_parentheses>
      <TOKEN>(</TOKEN>
      <nested_parentheses>
         <TOKEN>(</TOKEN>
         <tuple_sequence>
            <tuple>
               <digits>20</digits>
               <S> </S>
               <digits>35</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>10</digits>
               <S> </S>
               <digits>30</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>10</digits>
               <S> </S>
               <digits>10</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>30</digits>
               <S> </S>
               <digits>5</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>45</digits>
               <S> </S>
               <digits>20</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>20</digits>
               <S> </S>
               <digits>35</digits>
            </tuple>
         </tuple_sequence>
         <TOKEN>)</TOKEN>
      </nested_parentheses>
      <TOKEN>,</TOKEN>
      <S> </S>
      <nested_parentheses>
         <TOKEN>(</TOKEN>
         <tuple_sequence>
            <tuple>
               <digits>30</digits>
               <S> </S>
               <digits>20</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>20</digits>
               <S> </S>
               <digits>15</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>20</digits>
               <S> </S>
               <digits>25</digits>
            </tuple>
            <TOKEN>,</TOKEN>
            <S> </S>
            <tuple>
               <digits>30</digits>
               <S> </S>
               <digits>20</digits>
            </tuple>
         </tuple_sequence>
         <TOKEN>)</TOKEN>
      </nested_parentheses>
      <TOKEN>)</TOKEN>
   </nested_parentheses>
   <TOKEN>)</TOKEN>
</nested_parentheses>