/*
 * Name: Mike Cifelli
 * Course: CIS 443 - Programming Languages
 * Assignment: Lisp Parser
 */

package parser;

/**
 * This is the base class for memory in the PL-Lisp implementation.
 */
public class SExpression {

    // for mark and sweep garbage collection
    private boolean marked = false;

    /**
     * Determine if this <code>SExpression</code> is marked.
     *
     * @return
     *  <code>true</code> if this <code>SExpression</code> is marked;
     *  <code>false</code> otherwise
     */
    public final boolean isMarked() {
        return marked;
    }

    /**
     * Set the marked status of this S-expression to the specified value.
     *
     * @param value
     *  the value to assign to this S-expression's marked status
     */
    public final void setMarked(final boolean value) {
        marked = value;
    }

    // Lisp type predicates;
    // by default, all return false (an SExpression effectively has NO type);
    // overridden in subclasses to describe their Lisp type

    /**
     * Test if this S-expression is NULL.
     *
     * @return
     *  <code>false</code>
     */
    public boolean nullp() {
        return false;
    }

    /**
     * Test if this S-expression is an ATOM.
     *
     * @return
     *  <code>false</code>
     */
    public boolean atomp() {
        return false;
    }

    /**
     * Test if this S-expression is a CONS cell.
     *
     * @return
     *  <code>false</code>
     */
    public boolean consp() {
        return false;
    }

    /**
     * Test if this S-expression is a LIST.
     *
     * @return
     *  the value of <code>(consp() || nullp())</code>
     */
    public boolean listp() {
        return (consp() || nullp());
    }

    /**
     * Test if this S-expression is a NUMBER.
     *
     * @return
     *  <code>false</code>
     */
    public boolean numberp() {
        return false;
    }

    /**
     * Test if this S-expression is a SYMBOL.
     *
     * @return
     *  <code>false</code>
     */
    public boolean symbolp() {
        return false;
    }

    /**
     * Test if this S-expression is a FUNCTION.
     *
     * @return
     *  <code>false</code>
     */
    public boolean functionp() {
        return false;
    }

    /**
     * Test if this S-expression is a STRING.
     *
     * @return
     *  <code>false</code>
     */
    public boolean stringp() {
        return false;
    }

}