Throw_c.java

package polyglot.ext.jl.ast;

import polyglot.ast.*;

import polyglot.util.*;
import polyglot.types.*;
import polyglot.visit.*;
import java.util.*;

/**
 * A <code>Throw</code> is an immutable representation of a <code>throw</code>
 * statement. Such a statement contains a single <code>Expr</code> which
 * evaluates to the object being thrown.
 */
public class Throw_c extends Stmt_c implements Throw
{
    protected Expr expr;

    public Throw_c(Position pos, Expr expr) {
	super(pos);
	this.expr = expr;
    }

    /** Get the expression to throw. */
    public Expr expr() {
	return this.expr;
    }

    /** Set the expression to throw. */
    public Throw expr(Expr expr) {
	Throw_c n = (Throw_c) copy();
	n.expr = expr;
	return n;
    }

    /** Reconstruct the statement. */
    protected Throw_c reconstruct(Expr expr) {
	if (expr != this.expr) {
	    Throw_c n = (Throw_c) copy();
	    n.expr = expr;
	    return n;
	}

	return this;
    }

    /** Visit the children of the statement. */
    public Node visitChildren(NodeVisitor v) {
	Expr expr = (Expr) visitChild(this.expr, v);
	return reconstruct(expr);
    }

    /** Type check the statement. */
    public Node typeCheck(TypeChecker tc) throws SemanticException {
	if (! expr.type().isThrowable()) {
	    throw new SemanticException(
		"Can only throw subclasses of \"" +
		tc.typeSystem().Throwable() + "\".", expr.position());
	}

	return this;
    }

    public Type childExpectedType(Expr child, AscriptionVisitor av) {
        TypeSystem ts = av.typeSystem();

        if (child == expr) {
            return ts.Throwable();
        }

        return child.type();
    }

    public String toString() {
	return "throw " + expr + ";";
    }

    /** Write the statement to an output file. */
    public void prettyPrint(CodeWriter w, PrettyPrinter tr) {
	w.write("throw ");
	print(expr, w, tr);
	w.write(";");
    }

    public Term entry() {
        return expr.entry();
    }

    public List acceptCFG(CFGBuilder v, List succs) {
        v.visitCFG(expr, this);

        // Throw edges will be handled by visitor.
        return Collections.EMPTY_LIST;
    }

    public List throwTypes(TypeSystem ts) {
        // if the exception that a throw statement is given to throw is null,
        // then a NullPointerException will be thrown.
        return CollectionUtil.list(expr.type(), ts.NullPointerException());
    }
}