JavaScript的表达式解析器-5. 操作符的实现

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整个结构建立好之后，操作符的实现就相当的简单了。

以左移操作为例：

var igame;importNamespace( 'igame.Expression' );igame.Expression.Operator.ShiftLeft = function (){igame.Expression.Operator.BinaryOperator.call( this );this.setToken( '<<' );}with ( igame.Expression ){ClassDerive( Operator.ShiftLeft, 'ShiftLeft', Operator.BinaryOperator );Operator.ShiftLeft.prototype.evaluate = function ( operands ){Operator.BinaryOperator.prototype.evaluate.call( this, operands );var op2 = operands.pop();var op1 = operands.pop();if ( !( op2 instanceof Operand.Number ) )op2 = new Operand.Number( op2.getValue() );if ( !( op1 instanceof Operand.Number ) )op1 = new Operand.Number( op1.getValue() );if ( op1.getValue() < 0 )throw new Error( 'Shift count less than 0' );return new Operand.Number( op1.getValue() << op2.getValue() );}} // with igame

当然还要适当的修改操作符的优先级。优先级定义在Operator.js中。

/*! Define operators' priority* Use classname, not token(or operator)*/igame.Expression.Operator.OPERATOR_PRIORITY = {// Logic'Or': 0,'And': 0,// Compare'Greater': 1,'GreaterEqual': 1,'Equal': 1,'NotEquual': 1,'Less': 1,'LessEqual': 1,// Bitwise'BitwiseOr': 2,'BitwiseAnd': 2,'BitwiseXor': 2,// Mathematic'Add': 3,'Sub': 3,'Mul': 4,'Div': 4,'Mod': 4,'ShiftLeft': 4,'ShiftRight': 4,// Function'Function': 5,// Unary'Minus': 6,'Plus': 6,'Not': 6};