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A modified version of the GGP-Base library for Alloy.

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package org.ggp.base.util.gdl.grammar;

import java.util.List;

import com.google.common.collect.ImmutableList;

public final class GdlRule extends Gdl
{
    private static final long serialVersionUID = 1L;

    private final ImmutableList body;
    private transient Boolean ground;
    private final GdlSentence head;

    GdlRule(GdlSentence head, ImmutableList body)
    {
        this.head = head;
        this.body = body;
        ground = null;
    }

    public int arity()
    {
        return body.size();
    }

    private Boolean computeGround()
    {
        for (GdlLiteral literal : body)
        {
            if (!literal.isGround())
            {
                return false;
            }
        }

        return true;
    }

    public GdlLiteral get(int index)
    {
        return body.get(index);
    }

    public GdlSentence getHead()
    {
        return head;
    }

    public List getBody()
    {
        return body;
    }

    @Override
    public boolean isGround()
    {
        if (ground == null)
        {
            ground = computeGround();
        }

        return ground;
    }

    @Override
    public String toString()
    {
        StringBuilder sb = new StringBuilder();

        sb.append("( <= " + head + " ");
        for (GdlLiteral literal : body)
        {
            sb.append(literal + " ");
        }
        sb.append(")");

        return sb.toString();
    }

}