public void rollback(String programName, int instructionIndex) {
		List<RewriteOperation> is = programs.get(programName);
		if ( is!=null ) {
			programs.put(programName, is.subList(MIN_TOKEN_INDEX,instructionIndex));
		}
	}
Rollback the instruction stream for a program so that
 the indicated instruction (via instructionIndex) is no
 longer in the stream. UNTESTED!
runtime/Java/src/org/antlr/v4/runtime/TokenStreamRewriter.java