Package com.gengoai.parsing

Class Evaluator<O>

java.lang.Object

com.gengoai.parsing.Evaluator<O>

Type Parameters:

O - the type parameter

All Implemented Interfaces:

Serializable

public abstract class Evaluator<O>
extends Object
implements Serializable

An evaluator provides a switch-like interface for evaluating expressions. Custom evaluators can be created as follows:

 

 Evaluator<Double> eval = new Evaluator<Double>() {{
      $(BinaryOperatorExpression.class, CommonTypes.PLUS, e -> eval(e.left) + eval(e.right));
      $(ValueExpression.class, e -> Double.valueOf(e.toString()));
 }}

 
 

The various $ methods allow easily adding if-like predicates and then-like functions. The eval(Expression) method can be used to make recursive evaluation calls.

Author:

David B. Bracewell

See Also:

Serialized Form

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	Evaluator()	Instantiates a new Evaluator.

Method Summary

Modifier and Type	Method	Description
protected <E extends Expression> void	$(@NonNull Class<E> expressionClass, @NonNull Tag type, @NonNull CheckedFunction<E,? extends O> function)	Adds a switch statement where the condition is that the expression is of type expressionClass and the expressions's token type is an instance of type.
protected <E extends Expression> void	$(Class<E> expressionClass, CheckedFunction<E,? extends O> function)	Adds a switch statement where the condition is that the expression is of type expressionClass.
O	eval(Expression expression)	Evaluates the given expression

Methods inherited from class java.lang.Object

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

Constructor Detail

Evaluator

protected Evaluator()

Instantiates a new Evaluator.

Method Detail

$

protected final <E extends Expression> void $(@NonNull
                                              @NonNull Class<E> expressionClass,
                                              @NonNull
                                              @NonNull Tag type,
                                              @NonNull
                                              @NonNull CheckedFunction<E,? extends O> function)

Adds a switch statement where the condition is that the expression is of type expressionClass and the expressions's token type is an instance of type. When the condition is met the expression is cast as the given expression class and the given function is applied.

Type Parameters:

E - the type of expression

Parameters:

expressionClass - the expression class

type - the token type

function - the function to apply when the condition is met.

$

protected final <E extends Expression> void $(Class<E> expressionClass,
                                              CheckedFunction<E,? extends O> function)

Adds a switch statement where the condition is that the expression is of type expressionClass. When the condition is met the expression is cast as the given expression class and the given function is applied.

Type Parameters:

E - the type of expression

Parameters:

expressionClass - the expression class

function - the function to apply when the condition is met.

eval

public final O eval(Expression expression)
             throws ParseException

Evaluates the given expression

Parameters:

expression - the expression to evaluate

Returns:

the result of evaluation

Throws:

ParseException - Something went wrong during evaluation