civquest.parser.condition
Class ConditionParser

java.lang.Object
  civquest.parser.condition.ConditionParser

Direct Known Subclasses:

ComplexConditionParser, SimpleConditionParser

public abstract class ConditionParser

extends java.lang.Object

A ConditionParser is capable of processing one-line boolean expressions in its own Java-like language, and evaluating their truth values. This is useful because Java has no built-in mechanism for evaluating strings of its own grammar, like the eval() functions of scripting languages like Perl or Python. The partial grammar for the condition language looks like this:

 Operand ::= <Var> | <Int>
 RelOp   ::= '<' | '<=' | '=' | '>' | '>='
 Expr    ::= <Operand> <RelOp> <Operand>
           | '(' && ')'
           | '(' || ')'
 

In addition, although of less importance, line comments start with a ';' and block comments are embraced between '/*' and '*\/'. For referring to variables within the expressions, they must be bounded (passed to the parser in name/value pairs) prior to evaluation. This part is abstracted, to allow concrete sub-classes to deal with them in a manner most befitting its specialized purpose.

See Also:

SimpleConditionParser, ComplexConditionParser

Field Summary

protected Token	current
protected boolean	err
protected java.lang.String	expr
protected int	OP_AND
protected int	OP_EQ
protected int	OP_GE
protected int	OP_GT
protected int	OP_LE
protected int	OP_LT
protected int	OP_OR
protected civquest.parser.condition.ConditionTokenizer	tokenizer
protected civquest.parser.condition.BoolExpression	tree

Constructor Summary

ConditionParser(java.lang.String expr)
Creates a parser for the given expression, for which a parse-tree is immediately constructed.

Method Summary

abstract void	bind(java.lang.String name, int val) Binds a value to a variable name.
protected void	error(java.lang.String msg)
boolean	eval() Evaluates the expression according to the most recently bound values for variables.
abstract int	getBinding(java.lang.String name) Gets the value for a bound variable.
protected void	next()
protected civquest.parser.condition.BoolExpression	parseCompoundExpr()
protected civquest.parser.condition.BoolExpression	parseExpr()
protected int	parseLogicOperator()
protected civquest.parser.condition.AritExpression	parseOperand()
protected int	parseRelativeOperator()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

tokenizer

protected civquest.parser.condition.ConditionTokenizer tokenizer

current

protected Token current

err

protected boolean err

expr

protected java.lang.String expr

tree

protected civquest.parser.condition.BoolExpression tree

OP_EQ

protected final int OP_EQ

See Also:

Constant Field Values

OP_LT

protected final int OP_LT

See Also:

Constant Field Values

OP_LE

protected final int OP_LE

See Also:

Constant Field Values

OP_GT

protected final int OP_GT

See Also:

Constant Field Values

OP_GE

protected final int OP_GE

See Also:

Constant Field Values

OP_AND

protected final int OP_AND

See Also:

Constant Field Values

OP_OR

protected final int OP_OR

See Also:

Constant Field Values

Constructor Detail

ConditionParser

public ConditionParser(java.lang.String expr)

Creates a parser for the given expression, for which a parse-tree is immediately constructed.

Parameters:

expr - The conditional expression to be evaluated.

Method Detail

bind

public abstract void bind(java.lang.String name,
                          int val)

Binds a value to a variable name. Note that a concrete ConditionParser may have other preferred means for this.

Parameters:

name - The name of the variable to be bound

val - The value to bind to the name

getBinding

public abstract int getBinding(java.lang.String name)

Gets the value for a bound variable. Note that a concrete ConditionParser may have other preferred means for this.

Parameters:

name - The name of the variable

Returns:

the current value for the variable

eval

public boolean eval()

Evaluates the expression according to the most recently bound values for variables.

Returns:

true if the condition holds, false otherwise.

parseExpr

protected civquest.parser.condition.BoolExpression parseExpr()

parseCompoundExpr

protected civquest.parser.condition.BoolExpression parseCompoundExpr()

parseOperand

protected civquest.parser.condition.AritExpression parseOperand()

parseLogicOperator

protected int parseLogicOperator()

parseRelativeOperator

protected int parseRelativeOperator()

error

protected void error(java.lang.String msg)

next

protected void next()