com.heirloomcomputing.epli.runtime

Class Goto

java.lang.Object

java.lang.Throwable

java.lang.Exception

java.lang.RuntimeException

com.heirloomcomputing.epli.runtime.Goto

All Implemented Interfaces:

java.io.Serializable

public class Goto
extends java.lang.RuntimeException

Goto - Elastic PL/I GOTO statement label represented as a Throwable object. when GOTOs reference a target that is outside the scope of the GOTO statement (i.e. within an enclosing procedure which called the procedure containing the GOTO statement) the Java code will bounce up (perhaps multiple) levels of nested procedures to the location of that outer label. Example, turn the following PL/I code:

 A: PROC OPTIONS(MAIN);
    B: PROC;
       ...
       C: E=3;
       ...
       IF (...) THEN GOTO C;
       ...
       IF (...) THEN GOTO D;
       ...
       D: E = 2;
       ...
       IF (...) THEN GOTO E;
    END B;
    ...
    CALL B;
    ...
    E: E=4;
    ...
 END A;
 

with scoped labels named "A:B:C" , "A:B:D" and "A:E" and generate code blocks roughly equivalent to:

 public class A {
    public void a() {
       ...
       e: try {
          e = 4;
       catch (Goto exception) {
          exception.rethrowIfNotMe("A:E")
       }
       ...
    } // end a
    private void b() {
       ...
       c: while (true) {
          e=3;
          ...
          if (...) continue c; // backward GOTO C
          ...
          break c;
       }
       d: {
          ...
          if (...) break d; // forward GOTO D
          ...
       }
       e=2;
       ...
       if (...) throw new Goto("A:E"); // outer GOTO E
    }
    public void main(String [] args) {
       ...
       a();
       ...
    }
 }
 

Author:

Heirloom Computing, Inc.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
Goto() Construct a Goto State
Goto(java.lang.String goToLabel) Construct a Goto Exception

Method Summary

Modifier and Type	Method and Description
boolean	isTarget(java.lang.String checkLabel) isTarget - return true if you are here or if this is a new Goto state (not looking for any target) and the parameter is null indicating that this block should be executed once
java.lang.String	label() Return the label used to create this Goto
Goto	rethrowIfNotFound() Do nothing if the goto state is null meaning that the GOTO label was found at some point by isTarget() and executed at least one LabeledBlock within the GOTO loop.
Goto	rethrowIfNotMe(java.lang.String checkLabel) Do nothing if the goto label matches this object's label, otherwise throw the condition

Methods inherited from class java.lang.Throwable

addSuppressed, fillInStackTrace, getCause, getLocalizedMessage, getMessage, getStackTrace, getSuppressed, initCause, printStackTrace, printStackTrace, printStackTrace, setStackTrace, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Goto

public Goto(java.lang.String goToLabel)

Construct a Goto Exception

Goto

public Goto()

Construct a Goto State

Method Detail

rethrowIfNotMe

public Goto rethrowIfNotMe(java.lang.String checkLabel)
                    throws Goto

Do nothing if the goto label matches this object's label, otherwise throw the condition

Parameters:

checkLabel - - the label to check against this label

Returns:

this to facilitate chaining

Throws:

this - Goto if this is not at this level

Goto

rethrowIfNotFound

public Goto rethrowIfNotFound()

Do nothing if the goto state is null meaning that the GOTO label was found at some point by isTarget() and executed at least one LabeledBlock within the GOTO loop. however, if not-null, that means we went through the entire GOTO loop without finding it. rethrow it in the hopes that this is an outer goto with a target defined higher in the procedure call-stack

Returns:

this to facilitate chaining

Throws:

this - if this label was not found at this GOTO loop

isTarget

public boolean isTarget(java.lang.String checkLabel)

isTarget - return true if you are here or if this is a new Goto state (not looking for any target) and the parameter is null indicating that this block should be executed once

Parameters:

checkLabel - - the canonical name of the label to check, may be null

Returns:

boolean true if the goto state is destined to stop and execute the following block

label

public java.lang.String label()

Return the label used to create this Goto

Returns:

this Goto's label