header {#include <iostream>}options {	language=Cpp;}class LangParser extends Parser;options {	buildAST=true;}tokens {	BLOCK; // imaginary token}block	:	LCURLY! ( statement )* RCURLY!		// add imaginary BLOCK node on top of statement list		{#block = #([BLOCK, "BLOCK"], #block);}	;statement	:	ID ASSIGN^ expr SEMI!	|	"if"^ LPAREN! expr RPAREN! statement		( "else"! statement )?	|	"while"^ LPAREN! expr RPAREN! statement	|!	b:block { statement_AST = #b; }		// do some manual tree returning	;// add an EXPR node on top of an expression// note that the two alternatives behave exactly// the same way.expr:!	id:ID		{#expr = #([EXPR,"EXPR"],#id);}	|	INT			{#expr = #([EXPR,"EXPR"],#expr);}	;class LangWalker extends TreeParser;block	:	#( BLOCK ( stat )+ )	;stat:	#("if" expr stat (stat)?)	|	#("while" expr stat)	|	expr	|	block	|	#( ASSIGN ID expr )	;expr:	#(	EXPR			(	a:ID	{std::cout << "found ID "<<a->getText() << std::endl;}			|	b:INT	{std::cout << "found INT "<<b->getText() << std::endl;}			)		 )	;class LangLexer extends Lexer;WS_	:	(' '	|	'\t'	|	'\n'	|	'\r')		{ _ttype = ANTLR_USE_NAMESPACE(antlr)Token::SKIP; }	;LPAREN:	'('	;RPAREN:	')'	;LCURLY:	'{'	;RCURLY:	'}'	;ASSIGN	:	'='	;SEMI:	';'	;protectedDIGIT	:	'0'..'9'	;INT	:	(DIGIT)+	;IDoptions {	testLiterals = true;}	:	('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'_'|DIGIT)*	;