org.scijava.parsington.eval

Interface Evaluator

All Known Subinterfaces:

StackEvaluator, StandardEvaluator, StandardStackEvaluator, StandardTreeEvaluator, TreeEvaluator

All Known Implementing Classes:

AbstractEvaluator, AbstractStandardEvaluator, DefaultStackEvaluator, DefaultTreeEvaluator

public interface Evaluator

Interface for expression evaluators.

Author:

Curtis Rueden

Method Summary

Modifier and Type	Method and Description
Object	evaluate(LinkedList<Object> queue) Evaluates a postfix token queue.
Object	evaluate(String expression) Evaluates an infix expression.
Object	evaluate(SyntaxTree syntaxTree) Evaluates a syntax tree.
Object	get(Variable v) Gets the value of a variable.
ExpressionParser	getParser() Gets the parser used when evaluating expressions.
boolean	isStrict() Gets whether the evaluator is operating in strict mode.
void	set(Variable v, Object value) Sets the value of a variable.
void	setAll(Map<? extends String,? extends Object> map) Assigns variables en masse.
void	setStrict(boolean strict) Sets whether the evaluator is operating in strict mode.
default Object	value(Object token) Gets the value of a token.
default Variable	var(Object token) Casts the given token to a variable.

Method Detail

getParser

ExpressionParser getParser()

Gets the parser used when evaluating expressions.

Returns:

The expression parser used by this evaluator.

isStrict

boolean isStrict()

Gets whether the evaluator is operating in strict mode.

Returns:

True iff the evaluator is operating in strict mode.

See Also:

setStrict(boolean)

setStrict

void setStrict(boolean strict)

Sets whether the evaluator is operating in strict mode. Evaluators operate in strict mode by default.

When evaluating strictly, usage of an unassigned variable token in a place where its value is needed will generate an IllegalArgumentException with an "Unknown variable" message; in non-strict mode, such a variable will instead be resolved to an object of type Unresolved with the same name as the original variable.

In cases such as assignment, this may be sufficient to complete the evaluation; for example, the expression foo=bar will complete successfully in non-strict mode, with the variable foo containing an object of type Unresolved and token value "bar". But in cases where the unresolved value is needed as an input for additional operations, the evaluation may still ultimately fail of the operation in question is not defined for unresolved values. For example, the DefaultStackEvaluator will fail with an "Unsupported binary operator" exception when given the expression foo+bar, since foo and bar are unresolved variables, and the + operator cannot handle such objects.

Parameters:

strict - True iff the evaluator should operate in strict mode.

evaluate

Object evaluate(String expression)

Evaluates an infix expression.

Parameters:

expression - The infix expression to evaluate.

Returns:

The result of the evaluation.

evaluate

Object evaluate(LinkedList<Object> queue)

Evaluates a postfix token queue.

Parameters:

queue - The postfix token queue to evaluate.

Returns:

The result of the evaluation.

evaluate

Object evaluate(SyntaxTree syntaxTree)

Evaluates a syntax tree.

Parameters:

syntaxTree - The syntax tree to evaluate.

Returns:

The result of the evaluation.

value

default Object value(Object token)

Gets the value of a token. For variables, returns the value of the variable, throwing an exception if the variable is not set. For literals, returns the token itself.

Parameters:

token - The token whose value you want.

Returns:

The token's value.

var

default Variable var(Object token)

Casts the given token to a variable.

Parameters:

token - The token to cast to a Variable.

Returns:

Variable representation of the token.

Throws:

IllegalArgumentException - if the given token is not a Variable.

get

Object get(Variable v)

Gets the value of a variable.

Parameters:

v - The variable whose value you want.

Returns:

The variable's value.

Throws:

IllegalArgumentException - If the variable's value is not set, and the evaluator is operating in strict mode.

set

void set(Variable v,
         Object value)

Sets the value of a variable.

Parameters:

v - The variable whose value you want to set.

value - The value to assign to the variable.

setAll

void setAll(Map<? extends String,? extends Object> map)

Assigns variables en masse.

Parameters:

map - A map from variable names to variable values.