@Override
	public long getValue(ParserWalker walker) throws MemoryAccessException {
		long val = getUnary().getValue(walker);
		return -val;
	}
Form new expression by taking twos complement of a PatternExpression
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/app/plugin/processors/sleigh/expression/MinusExpression.java