sjm.engine
Class Evaluation

java.lang.Object
  |
  +--sjm.engine.Structure
        |
        +--sjm.engine.Gateway
              |
              +--sjm.engine.Evaluation

public class Evaluation

extends Gateway

An Evaluation unifies a term with the value of another term.

For example,

     NumberFact two = new NumberFact(2);
     ArithmeticOperator x, y;
     x = new ArithmeticOperator('*', two, two);
     y = new ArithmeticOperator('+', x, two);
     
     Variable result = new Variable("Result");
     Evaluation e = new Evaluation(result, y);
     System.out.println(e);
     System.out.println(e.canFindNextProof());
     System.out.println(result);
     
 

prints out:

     #(Result, +(*(2.0, 2.0), 2.0))
     true
     6.0
 

Since an Evaluation unifies the first term with the arithmetic value, the second term may have a value before the Evaluation proves itself. In this case, the Evaluation checks that the second term's ground value equals the arithmetic value of the first term.

The Evaluation fails if the arithmetic value is invalid for any reason.

Field Summary

protected Unification

currentUnification

Fields inherited from class sjm.engine.Gateway

open

Fields inherited from class sjm.engine.Structure

emptyList, functor, terms

Constructor Summary

Evaluation(Term term0, Term term1)
Constructs an Evaluation that will unify the first term with the second term during proofs.

Method Summary

boolean	canProveOnce() Returns true if this Evaluation can unify its first term with the value of its second term.
protected void	cleanup() Insert the method's description here.
Term	copyForProof(AxiomSource ignored, Scope scope) Create a copy that uses the provided scope.
void	unbind() Releases the variable bindings that the last unification produced.

Methods inherited from class sjm.engine.Gateway

canFindNextProof

Methods inherited from class sjm.engine.Structure

arity, equals, eval, functorAndArityEquals, headAndTail, isList, list, list, list, listTailString, listTermsToString, terms, toString, unify, unify, unify, variables

Methods inherited from class java.lang.Object

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

Field Detail

currentUnification

protected Unification currentUnification

Constructor Detail

Evaluation

public Evaluation(Term term0,
                  Term term1)

Constructs an Evaluation that will unify the first term with the second term during proofs.

Parameters:

Term - the first term to unify

Term - the term whose value should unify with the first term

Method Detail

canProveOnce

public boolean canProveOnce()

Returns true if this Evaluation can unify its first term with the value of its second term.

If the attempt to evaluate the second term causes an exception, this method swallows it and simply fails.

Overrides:

canProveOnce in class Gateway

Returns:

true<, if this Evaluation can unify its first term with the arithmetic value of its second term

cleanup

protected void cleanup()

Description copied from class: Gateway

Insert the method's description here. Creation date: (12/7/99 11:09:44 AM)

Overrides:

cleanup in class Gateway

copyForProof

public Term copyForProof(AxiomSource ignored,
                         Scope scope)

Create a copy that uses the provided scope.

Overrides:

copyForProof in class Structure

Parameters:

AxiomSource - ignored

Scope - the scope to use for variables in the copy

Returns:

a copy that uses the provided scope

unbind

public void unbind()

Releases the variable bindings that the last unification produced.