{
  const n = options?.nodes;
  if (!n) {
    throw new Error('The parser expects a nodes module via options.nodes.');
  }
}

rules
  = statement+

statement
  = s:statement_type _ { return s }

statement_type
  = assignment
  / comment

comment
  = '#' v:[^\r\n]* [\r\n] { return new n.Comment(v.join('')) }

assignment
  = v:variable _ '=' _ e:expr _ ';' { return new n.Assignment(v, e) }

variable
  = v:name  { return new n.Variable(v) }

expr
  = alternation

alternation
  = a:concatenation _ '|' _ b:alternation     { return new n.Alternation(a, b) }
  / concatenation

concatenation
  = a:repeat _ b:concatenation           { return new n.Concatenation(a, b) }
  / repeat

repeat
  = t:name ':' e:repeat { return new n.Concatenation(e, new n.Tag(t)) }
  / t:term '*'  { return new n.Repeat(t, '*') }
  / t:term '?'  { return new n.Repeat(t, '?') }
  / t:term '+'  { return new n.Repeat(t, '+') }
  / t:term '{' m:number '}' { return n.buildRepetition(t, m, m) }
  / t:term '{' min:number ',' '}' { return n.buildRepetition(t, min, Infinity) }
  / t:term '{' ',' max:number '}' { return n.buildRepetition(t, 0, max) }
  / t:term '{' min:number ',' max:number '}' { return n.buildRepetition(t, min, max) }
  / term

term
  = variable
  / x:number { return new n.Literal(x) }
  / '(' e:expr ')' { return e }

repetition
  = '{' number '}' { return n.buildRepetition() }

name
  = a:name_start_char b:name_char* { return a + b.join('') }

name_start_char
  = "_"
  / [a-zA-Z]

name_char
  = name_start_char
  / [0-9]

number
  = num:[0-9]+  { return parseInt(num.join('')) }

_
  = [ \t\r\n]*