package pattpack.ast_vis3;

/**
 *  This class interprets a program by means of a Visitor pattern.
 */

public class InterpretVisitor implements Visitor {

    pattpack.expr_vis3.InterpretVisitor eval = new pattpack.expr_vis3.InterpretVisitor ();

    /**
     *  Interpret an Assignment statement.
     *  @param o  Ignored
     *  @return Null
     */
    public Object visit (Assignment s, Object o) {
	int value = ((Integer) s.getRvalue ().accept (eval, null)).intValue ();
	s.getLvalue ().setValue (value);
	return null;
    }
    /**
     *  Interpret an Compound statement.
     *  @param o  Ignored
     *  @return Null
     */
    public Object visit (Compound s, Object o) {
	Statement [] body = s.getBody ();
	for (int i = 0; i < body.length; i++) body [i].accept (this, o);
	return null;
    }
    /**
     *  Interpret an Conditional statement.
     *  @param o  Ignored
     *  @return Null
     */
    public Object visit (Conditional s, Object o) {
	if (((Integer) s.getTest ().accept (eval, null)).intValue () == 1)
	    s.getThenClause ().accept (this, o);
	else
	    s.getElseClause ().accept (this, o);
	return null;
    }
    /**
     *  Interpret an Output statement.
     *  @param o  Ignored
     *  @return Null
     */
    public Object visit (Output s, Object o) {
	System.out.println (s.getExpr ().accept (eval, null));
	return null;
    }
    /**
     *  Interpret an While statement.
     *  @param o  Ignored
     *  @return Null
     */
    public Object visit (While s, Object o) {
	while (((Integer) s.getTest ().accept (eval, null)).intValue () == 1)
	    s.getBody ().accept (this, o);
	return null;
    }
}