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Truffle is a multi-language framework for executing dynamic languages that achieves high performance when combined with Graal.
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package com.oracle.truffle.api.nodes;

import com.oracle.truffle.api.TruffleRuntime;
import com.oracle.truffle.api.frame.VirtualFrame;

/**
 * A node that is repeatedly invoked as part of a Truffle loop control structure. Repeating nodes
 * must extend {@link Node} or a subclass of {@link Node}.
 *
 * Repeating nodes are intended to be implemented by guest language implementations. For a full
 * usage example please see {@link LoopNode}.
 *
 * @see LoopNode
 * @see TruffleRuntime#createLoopNode(RepeatingNode)
 * @since 0.8 or earlier
 */
public interface RepeatingNode extends NodeInterface {
    /**
     * A value indicating that the loop should be repeated.
     *
     * @since 19.3
     */
    Object CONTINUE_LOOP_STATUS = new Object() {
        @Override
        public String toString() {
            return "CONTINUE_LOOP_STATUS";
        }
    };

    /**
     * A value indicating that the loop should not be repeated. Any other value different than
     * {@code CONTINUE_LOOP_STATUS} can also be used to indicate that the loop should not be
     * repeated.
     *
     * @since 19.3
     */
    Object BREAK_LOOP_STATUS = new Object() {
        @Override
        public String toString() {
            return "BREAK_LOOP_STATUS";
        }
    };

    /**
     * Repeatedly invoked by a {@link LoopNode loop node} implementation until the method returns
     * false or throws an exception.
     *
     * @param frame the current execution frame passed through the interpreter
     * @return true if the method should be executed again to complete the loop and
     *         false if it must not.
     * @since 0.8 or earlier
     */
    boolean executeRepeating(VirtualFrame frame);

    /**
     * Repeatedly invoked by a {@link LoopNode loop node} implementation, but allows returning a
     * language-specific loop exit status. Only languages that need to return custom loop statuses
     * should override this method.
     *
     * @param frame the current execution frame passed through the interpreter
     * @return a value v satisfying {@link RepeatingNode#shouldContinue
     *         shouldContinue(v)} == true if the method should be executed again to
     *         complete the loop and any other value if it must not.
     * @since 19.3
     */
    default Object executeRepeatingWithValue(VirtualFrame frame) {
        if (executeRepeating(frame)) {
            return CONTINUE_LOOP_STATUS;
        } else {
            return BREAK_LOOP_STATUS;
        }
    }

    /**
     * Returns a placeholder loop status used internally before the first iteration.
     *
     * @return a value satisfying
     *         {@link RepeatingNode#shouldContinue shouldContinue}({@link RepeatingNode#initialLoopStatus initialLoopStatus}(v)) == true
     * @since 20.3
     */
    default Object initialLoopStatus() {
        return CONTINUE_LOOP_STATUS;
    }

    /**
     * Predicate called on values returned by
     * {@link RepeatingNode#executeRepeatingWithValue(VirtualFrame) executeRepeatingWithValue()}.
     *
     * @param returnValue a value returned by
     *            {@link RepeatingNode#executeRepeatingWithValue(VirtualFrame)
     *            executeRepeatingWithValue()}
     * @return true if the loop should continue executing or false otherwise
     * @since 20.3
     */
    default boolean shouldContinue(Object returnValue) {
        return returnValue == initialLoopStatus();
    }
}