code: private Expression compileUnary(UnaryOperation unary, int opPos)
            throws TransformerException
    {
  
      int rightPos = getFirstChildPos(opPos);
  
      unary.setRight(compile(rightPos));
  
      return unary;
    }
docs: Bottle-neck compilation of a unary operation.
  
  @param unary The parent unary operation.
  @param opPos The position in the op map of the parent operation.
  
  @return The unary argument.
  
  @throws TransformerException if syntax or other error occurs.