grammar        = -
               ( d:definition                            { setInTopNamespace(d.name, d.expression); }
               ) + end-of-file

definition     = i:identifier ASSIGN e:expression SEMI?  { Definition.new(name: i, expression: e); }

expression     = s:sequence !BAR                         { s; }
               | s1:sequence                             { s1 = Alternation.new().push(s1); }
                 ( BAR s2:sequence                       { s1.push(s2); }
                 ) *                                     { s1; }

sequence       = p:prefix                                { p = Sequence.new().push(p); }
               ( q:prefix                                { p.push(q); }
               ) *                                       { p; }

prefix         = AND a:action                            { ParseTimeAction.new(action: a); }
               |
                 ( AND s:suffix                          { And.new(expression: s); }
                 | NOT s:suffix                          { Not.new(expression: s); }
                 | s:suffix                              { s; }
                 )

suffix         = p:primary
               ( QUERY                                   { p = Optional.new(expression: p); }
               | STAR                                    { p = Star.new(expression: p); }
               | PLUS                                    { p = Plus.new(expression: p); }
               ) ?                                       { p; }

primary        = i1:identifier COLON i2:ruleCall !ASSIGN { Assignment.new(name: i1, rule: i2); }
               | i:ruleCall !ASSIGN                      { i; }
               | LPAREN e:expression RPAREN              { e; }
               | l:literal                               { l; }
               | c:class                                 { c; }
               | DOT                                     { Dot.new(); }
               | a:action                                { a; }
               | BEGIN                                   { Begin.new(); }
               | END                                     { End.new(); }

identifier     = < [-a-zA-Z_][-a-zA-Z_0-9]* > -          { intern(yytext); }

ruleCall       = n:identifier CCOLON r:identifier        { NamespacedRuleCall.new(namespace: n, name: r); }
               | i:identifier                            { RuleCall.new(name: i); }

literal        = ['] < ( !['] char )* > ['] -            { StringLiteral.new(string: yytext); }
               | ["] < ( !["] char )* > ["] -            { StringLiteral.new(string: yytext); }

class          = '[' < ( !']' range )* > ']' -           { CharacterClass.new(value: yytext); }

range          = char '-' char | char

char           = '\\' [abefnrtv'"\[\]\\]
               | '\\' [0-3][0-7][0-7]
               | '\\' [0-7][0-7]?
               | !'\\' .

action         = m:metaLanguage::block -                 { Action.new(parseTree: m); }

-              = ( space | comment )*
space          = ' ' | '\t' | end-of-line
comment        = '#' ( !end-of-line . )* end-of-line
end-of-line    = '\r\n' | '\n' | '\r'
end-of-file    = !.

BAR            = '|'          -
NOT            = '!'          -
QUERY          = '?'          -
BEGIN          = '<'          -
END            = '>'          -
SEMI           = ";"          -
CCOLON         = "::"         -
LPAREN         = "("          -
RPAREN         = ")"          -
ASSIGN         = "=" ![=]     -
AND            = "&" ![&=]    -
PLUS           = "+" ![+=]    -
STAR           = "*" ![=]     -
DOT            = "." ![.]     -
COLON          = ":" ![:]     -