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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 Node or a subclass of Node. Repeating nodes are intended to be implemented by guest language implementations. For a full usage example please see LoopNode. 
See Also:
LoopNode
TruffleRuntime.createLoopNode(RepeatingNode)
Since:
0.8 or earlier/**
 * 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/**
     * 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 CONTINUE_LOOP_STATUS can also be used to indicate that the loop should not be repeated. 
Since:
19.3/**
     * 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 loop node implementation until the method returns false or throws an exception.
Params:
frame – the current execution frame passed through the interpreter
Returns:
true if the method should be executed again to complete the loop and
        false if it must not.
Since:
0.8 or earlier/**
     * Repeatedly invoked by a {@link LoopNode loop node} implementation until the method returns
     * <code>false</code> or throws an exception.
     *
     * @param frame the current execution frame passed through the interpreter
     * @return <code>true</code> if the method should be executed again to complete the loop and
     *         <code>false</code> if it must not.
     * @since 0.8 or earlier
     */
    boolean executeRepeating(VirtualFrame frame);

    
Repeatedly invoked by a 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. 
Params:
frame – the current execution frame passed through the interpreter
Returns:
a value v satisfying 
        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/**
     * 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 <code>v</code> satisfying {@link RepeatingNode#shouldContinue
     *         shouldContinue(v)}<code> == true</code> 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.
Returns:
a value satisfying
        shouldContinue(initialLoopStatus(v)) == true
Since:
20.3/**
     * Returns a placeholder loop status used internally before the first iteration.
     *
     * @return a value satisfying
     *         <code>{@link RepeatingNode#shouldContinue shouldContinue}({@link RepeatingNode#initialLoopStatus initialLoopStatus}(v)) == true</code>
     * @since 20.3
     */
    default Object initialLoopStatus() {
        return CONTINUE_LOOP_STATUS;
    }

    
Predicate called on values returned by executeRepeatingWithValue(). 
Params:
returnValue – a value returned by 
           executeRepeatingWithValue()
Returns:
true if the loop should continue executing or false otherwise
Since:
20.3/**
     * 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();
    }
}