chars.md

layout	title
default	Character classes

Character classes

Character classes work just like their counterparts from regular expressions, in fact they literally get compiled into identical regexes in the parser.

For example, this grammar matches a single alphanumeric character:

alphanum.peg

grammar Alphanum
  root  <-  [A-Za-z0-9]

This will parse any character matched by the class, and no others:

require('./alphanum').parse('a')
   == { text: 'a', offset: 0, elements: [] }

require('./alphanum').parse('7')
   == { text: '7', offset: 0, elements: [] }

require('./alphanum').parse('!')
SyntaxError: Line 1: expected one of:

    - [A-Za-z0-9] from Alphanum::root

     1 | !
         ^

There is a special character class denoted by . (period). This matches any character.

anything.peg

grammar Anything
  root  <-  .

require('./anything').parse('a')
   == { text: 'a', offset: 0, elements: [] }