Common Lisp to Scheme translation
Help for translating the book's code to Scheme

In Common Lisp NIL is a defined symbol:

(define NIL '())

car of an empty list in Common Lisp returns NIL, the empty list again. car in Scheme does not return the empty list, but raises an error. This means, that, for compatibility reasons, we have to write a little procedure, which acts like car from Common Lisp:

(define NIL '())

(define car/nil
  (lambda (possibly-empty-list)
    "In Common Lisp car of an empty list returns the empty list called NIL. In
Scheme it would be an error to call car on an empty list. We write a wrapper, to
avoid an error."
    (cond
     [(null? possibly-empty-list) NIL]
     [else (car possibly-empty-list)])))

rest in Common Lisp also returns NIL, when called with the empty list as argument, so a wrapper is needed:

(define NIL '())

(define rest
  (lambda (lst)
    (cond
     [(null? lst) NIL]
     [else (cdr lst)])))

A parameter is explained in the book as a binding, that usually does not chance, a constant. A change to it is explained as a change to the program, not a change by the program, in contrast to using defvar.

Since in Scheme we usually try to avoid using assignment or set! anyway, we can get away with following a convention of naming constants with enclosing asterisks: *constant* and using define.

???