3301

Ben Bitdiddle and Alyssa P. Hacker disagree over the importance of lazy evaluationfor implementing things such as unless. Ben points out that it’s possible to implement unless inapplicative order as a special form. Alyssa counters that, if one did that, unless would be merelysyntax, not a procedure that could be used in conjunction with higher-order procedures. Fill in thedetails on both sides of the argument. Show how to implement unless as a derived expression (likecond or let), and give an example of a situation where it might be useful to have unless availableas a procedure, rather than as a special form.