Repeated nodes

Canopy offers the well-known * and + operators from regular expressions, meaning “zero or more” and “one or more” respectively. Placing them after a node allows the node to repeat the desired number of times.

Here’s a grammar that matches the word badger one or more times:

badger.peg

grammar Badger
  root  <-  "badger"+

When a repetition matches the input, you get one node for the repetition itself, and one child node for each instance in the repetition. If there aren’t enough repetitions (for example if there’s not at least one match for a + rule) you’ll get an error.

require('./badger').parse('badgerbadgerbadger')
   == { text: 'badgerbadgerbadger',
        offset: 0,
        elements: [
          { text: 'badger', offset: 0, elements: [] },
          { text: 'badger', offset: 6, elements: [] },
          { text: 'badger', offset: 12, elements: [] }
        ] }

require('./badger').parse('bad')
SyntaxError: Line 1: expected one of:

    - "badger" from Badger::root

     1 | bad
         ^

Canopy also supports numeric repetition, which takes the following forms:

• expr{n} matches expr exactly n times
• expr{n,} matches expr at least n times
• expr{n,m} matches expr at least n times and at most m times

For example, this grammar accepts the word badger repeated 3, 4 or 5 times:

badger.peg

grammar Badger
  root  <-  "badger"{3,5}