This is very, very, very bad scheme. set! and list-ref are no-no.
This is better scheme:
(define (pascal n) (if (= n 0) (list 1) (let ((L (pascal (- n 1)))) (append (list 1) (map + (cdr L) L) (list 1)))))
This is better scheme:
(define (pascal n) (if (= n 0) (list 1) (let ((L (pascal (- n 1)))) (append (list 1) (map + (cdr L) L) (list 1)))))
As for your particular questions:
1. map yields an error under mzscheme
I'm at work, and didn't have access to a proper scheme, so I used an online REPL[1], which apparently is more forgiving. Regardless, you can write your own map (a good exercise!) that stops as soon as one of the arguments is exhausted. Make it tail-recursive[2] as well!
2. list-ref is bad
Lists are beautiful data structures designed for recursive algorithms. If you are using lists and not using recursion (or a hidden recursion in the form of map), you're doing something wrong. list-ref uses list as a vector, which has a performance implications - your algorithm is O(n^3) while mine is O(n^2).
3. set! is bad
Margins are too small for a proper explanation :), but basically set! has side-effects[3], and functional programming should avoid having them.
Have fun learning Scheme!
[0] http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-9.html#... [1] http://www.bluishcoder.co.nz/jsscheme/ [2] http://en.wikipedia.org/wiki/Tail_call [3] http://en.wikipedia.org/wiki/Side_effect_(computer_science)
(define next (lambda (l) (if (null? (cdr l)) '(1) (cons (+ (car l) (cadr l)) (next (cdr l))))))
(define pascal (lambda (n) (cond ((< n 1) '()) ((= n 1) '(1)) (else (cons 1 (next (pascal (- n 1))))))))