java.g

drools 一个开放源码的规则引擎

	;

// This is an initializer used to set up an array.
arrayInitializer
	:	lc:LCURLY^ {#lc.setType(ARRAY_INIT);}
			(	initializer
				(
					// CONFLICT: does a COMMA after an initializer start a new
					//           initializer or start the option ',' at end?
					//           ANTLR generates proper code by matching
					//			 the comma as soon as possible.
					options {
						warnWhenFollowAmbig = false;
					}
				:
					COMMA! initializer
				)*
				(COMMA!)?
			)?
		RCURLY!
	;


// The two "things" that can initialize an array element are an expression
//   and another (nested) array initializer.
initializer
	:	expression
	|	arrayInitializer
	;

// This is the header of a method.  It includes the name and parameters
//   for the method.
//   This also watches for a list of exception classes in a "throws" clause.
ctorHead
	:	IDENT  // the name of the method

		// parse the formal parameter declarations.
		LPAREN! parameterDeclarationList RPAREN!

		// get the list of exceptions that this method is declared to throw
		(throwsClause)?
	;

// This is a list of exception classes that the method is declared to throw
throwsClause
	:	"throws"^ identifier ( COMMA! identifier )*
	;


// A list of formal parameters
parameterDeclarationList
	:	( parameterDeclaration ( COMMA! parameterDeclaration )* )?
		{#parameterDeclarationList = #(#[PARAMETERS,"PARAMETERS"],
									#parameterDeclarationList);}
	;

// A formal parameter.
parameterDeclaration!
	:	pm:parameterModifier t:typeSpec[false] id:IDENT
		pd:declaratorBrackets[#t]
		{#parameterDeclaration = #(#[PARAMETER_DEF,"PARAMETER_DEF"],
									pm, #([TYPE,"TYPE"],pd), id);}
	;

parameterModifier
	:	(f:"final")?
		{#parameterModifier = #(#[MODIFIERS,"MODIFIERS"], f);}
	;

// Compound statement.  This is used in many contexts:
//   Inside a class definition prefixed with "static":
//      it is a class initializer
//   Inside a class definition without "static":
//      it is an instance initializer
//   As the body of a method
//   As a completely indepdent braced block of code inside a method
//      it starts a new scope for variable definitions

compoundStatement
	:	lc:LCURLY^ {#lc.setType(SLIST);}
			// include the (possibly-empty) list of statements
			(statement)*
		RCURLY!
	;


statement
	// A list of statements in curly braces -- start a new scope!
	:	compoundStatement

	// declarations are ambiguous with "ID DOT" relative to expression
	// statements.  Must backtrack to be sure.  Could use a semantic
	// predicate to test symbol table to see what the type was coming
	// up, but that's pretty hard without a symbol table ;)
	|	(declaration)=> declaration SEMI!

	// An expression statement.  This could be a method call,
	// assignment statement, or any other expression evaluated for
	// side-effects.
	|	expression SEMI!

	// class definition
	|	m:modifiers! classDefinition[#m]

	// Attach a label to the front of a statement
	|	IDENT c:COLON^ {#c.setType(LABELED_STAT);} statement

	// If-else statement
	|	"if"^ LPAREN! expression RPAREN! statement
		(
			// CONFLICT: the old "dangling-else" problem...
			//           ANTLR generates proper code matching
			//			 as soon as possible.  Hush warning.
			options {
				warnWhenFollowAmbig = false;
			}
		:
			"else"! statement
		)?

	// For statement
	|	"for"^
			LPAREN!
				forInit SEMI!   // initializer
				forCond	SEMI!   // condition test
				forIter         // updater
			RPAREN!
			statement                     // statement to loop over

	// While statement
	|	"while"^ LPAREN! expression RPAREN! statement

	// do-while statement
	|	"do"^ statement "while"! LPAREN! expression RPAREN! SEMI!

	// get out of a loop (or switch)
	|	"break"^ (IDENT)? SEMI!

	// do next iteration of a loop
	|	"continue"^ (IDENT)? SEMI!

	// Return an expression
	|	"return"^ (expression)? SEMI!

	// switch/case statement
	|	"switch"^ LPAREN! expression RPAREN! LCURLY!
			( casesGroup )*
		RCURLY!

	// exception try-catch block
	|	tryBlock

	// throw an exception
	|	"throw"^ expression SEMI!

	// synchronize a statement
	|	"synchronized"^ LPAREN! expression RPAREN! compoundStatement

	// empty statement
	|	s:SEMI {#s.setType(EMPTY_STAT);}
	;


casesGroup
	:	(	// CONFLICT: to which case group do the statements bind?
			//           ANTLR generates proper code: it groups the
			//           many "case"/"default" labels together then
			//           follows them with the statements
			options {
				warnWhenFollowAmbig = false;
			}
			:
			aCase
		)+
		caseSList
		{#casesGroup = #([CASE_GROUP, "CASE_GROUP"], #casesGroup);}
	;

aCase
	:	("case"^ expression | "default") COLON!
	;

caseSList
	:	(statement)*
		{#caseSList = #(#[SLIST,"SLIST"],#caseSList);}
	;

// The initializer for a for loop
forInit
		// if it looks like a declaration, it is
	:	(	(declaration)=> declaration
		// otherwise it could be an expression list...
		|	expressionList
		)?
		{#forInit = #(#[FOR_INIT,"FOR_INIT"],#forInit);}
	;

forCond
	:	(expression)?
		{#forCond = #(#[FOR_CONDITION,"FOR_CONDITION"],#forCond);}
	;

forIter
	:	(expressionList)?
		{#forIter = #(#[FOR_ITERATOR,"FOR_ITERATOR"],#forIter);}
	;

// an exception handler try/catch block
tryBlock
	:	"try"^ compoundStatement
		(handler)*
		( "finally"^ compoundStatement )?
	;


// an exception handler
handler
	:	"catch"^ LPAREN! parameterDeclaration RPAREN! compoundStatement
	;


// expressions
// Note that most of these expressions follow the pattern
//   thisLevelExpression :
//       nextHigherPrecedenceExpression
//           (OPERATOR nextHigherPrecedenceExpression)*
// which is a standard recursive definition for a parsing an expression.
// The operators in java have the following precedences:
//    lowest  (13)  = *= /= %= += -= <<= >>= >>>= &= ^= |=
//            (12)  ?:
//            (11)  ||
//            (10)  &&
//            ( 9)  |
//            ( 8)  ^
//            ( 7)  &
//            ( 6)  == !=
//            ( 5)  < <= > >=
//            ( 4)  << >>
//            ( 3)  +(binary) -(binary)
//            ( 2)  * / %
//            ( 1)  ++ -- +(unary) -(unary)  ~  !  (type)
//                  []   () (method call)  . (dot -- identifier qualification)
//                  new   ()  (explicit parenthesis)
//
// the last two are not usually on a precedence chart; I put them in
// to point out that new has a higher precedence than '.', so you
// can validy use
//     new Frame().show()
// 
// Note that the above precedence levels map to the rules below...
// Once you have a precedence chart, writing the appropriate rules as below
//   is usually very straightfoward



// the mother of all expressions
expression
	:	assignmentExpression
		{#expression = #(#[EXPR,"EXPR"],#expression);}
	;


// This is a list of expressions.
expressionList
	:	expression (COMMA! expression)*
		{#expressionList = #(#[ELIST,"ELIST"], expressionList);}
	;


// assignment expression (level 13)
assignmentExpression
	:	conditionalExpression
		(	(	ASSIGN^
            |   PLUS_ASSIGN^
            |   MINUS_ASSIGN^
            |   STAR_ASSIGN^
            |   DIV_ASSIGN^
            |   MOD_ASSIGN^
            |   SR_ASSIGN^
            |   BSR_ASSIGN^
            |   SL_ASSIGN^
            |   BAND_ASSIGN^
            |   BXOR_ASSIGN^
            |   BOR_ASSIGN^
            )
			assignmentExpression
		)?
	;


// conditional test (level 12)
conditionalExpression
	:	logicalOrExpression
		( QUESTION^ assignmentExpression COLON! conditionalExpression )?
	;


// logical or (||)  (level 11)
logicalOrExpression
	:	logicalAndExpression (LOR^ logicalAndExpression)*
	;


// logical and (&&)  (level 10)
logicalAndExpression
	:	inclusiveOrExpression (LAND^ inclusiveOrExpression)*
	;


// bitwise or non-short-circuiting or (|)  (level 9)
inclusiveOrExpression
	:	exclusiveOrExpression (BOR^ exclusiveOrExpression)*
	;


// exclusive or (^)  (level 8)
exclusiveOrExpression
	:	andExpression (BXOR^ andExpression)*
	;


// bitwise or non-short-circuiting and (&)  (level 7)
andExpression
	:	equalityExpression (BAND^ equalityExpression)*
	;


// equality/inequality (==/!=) (level 6)
equalityExpression
	:	relationalExpression ((NOT_EQUAL^ | EQUAL^) relationalExpression)*
	;


// boolean relational expressions (level 5)
relationalExpression
	:	shiftExpression
		(	(	(	LT^
				|	GT^
				|	LE^
				|	GE^
				)
				shiftExpression
			)*
		|	"instanceof"^ typeSpec[true]
		)
	;


// bit shift expressions (level 4)
shiftExpression
	:	additiveExpression ((SL^ | SR^ | BSR^) additiveExpression)*
	;


// binary addition/subtraction (level 3)
additiveExpression
	:	multiplicativeExpression ((PLUS^ | MINUS^) multiplicativeExpression)*
	;


// multiplication/division/modulo (level 2)
multiplicativeExpression
	:	unaryExpression ((STAR^ | DIV^ | MOD^ ) unaryExpression)*
	;

unaryExpression
	:	INC^ unaryExpression
	|	DEC^ unaryExpression
	|	MINUS^ {#MINUS.setType(UNARY_MINUS);} unaryExpression
	|	PLUS^  {#PLUS.setType(UNARY_PLUS);} unaryExpression
	|	unaryExpressionNotPlusMinus
	;

unaryExpressionNotPlusMinus
	:	BNOT^ unaryExpression
	|	LNOT^ unaryExpression

	|	(	// subrule allows option to shut off warnings
			options {
				// "(int" ambig with postfixExpr due to lack of sequence
				// info in linear approximate LL(k).  It's ok.  Shut up.
				generateAmbigWarnings=false;
			}
		:	// If typecast is built in type, must be numeric operand
			// Also, no reason to backtrack if type keyword like int, float...
			lpb:LPAREN^ {#lpb.setType(TYPECAST);} builtInTypeSpec[true] RPAREN!
			unaryExpression

			// Have to backtrack to see if operator follows.  If no operator
			// follows, it's a typecast.  No semantic checking needed to parse.
			// if it _looks_ like a cast, it _is_ a cast; else it's a "(expr)"
		|	(LPAREN classTypeSpec[true] RPAREN unaryExpressionNotPlusMinus)=>
			lp:LPAREN^ {#lp.setType(TYPECAST);} classTypeSpec[true] RPAREN!
			unaryExpressionNotPlusMinus

		|	postfixExpression
		)
	;

// qualified names, array expressions, method invocation, post inc/dec
postfixExpression
	:	primaryExpression // start with a primary

		(	// qualified id (id.id.id.id...) -- build the name
			DOT^ ( IDENT
				| "this"
				| "class"
				| newExpression
				| "super" // ClassName.super.field
				)
			// the above line needs a semantic check to make sure "class"
			// is the _last_ qualifier.