This one drove me crazy because of the requirement to return -1 if s not in los.
(list-index s los) returns the zero-based index of the first occurence of s in los, or -1 if there is no occurences of s in los.
- (define list-index
- (lambda (s los)
- (if (null? los)
- (if (eq? (car los) s)
- (if (= (list-index s (cdr los)) -1)
- (+ 1 (list-index s (cdr los))))))))
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