Before revision:  However, existing HCI methods expect iteration with appropriate users, who must learn to use the language to be evaluated. These methods were impractical to apply to programming languages: they have high iteration costs, programmers require significant learning time, and user performance has high variance.
After revision:  However, existing HCI methods can be impractical to apply to programming languages: they have high iteration costs, programmers require significant learning time, and user performance has high variance.