"Ignore" is easier said than done. Students make mistakes. They type the wrong character. They put something in thew wrong place. If you don't enforce your sub-

"Ignore" is easier said than done. Students make mistakes. They type the wrong character. They put something in thew wrong place. If you don't enforce your sub-language, you are effectively throwing them into the open, and they suffer. We've seen numerous examples of this, which is why DrRacket offers teaching languages that are subsets of the full language, with customized errors that match the student's vocabulary and level of understanding, etc.