From Newsgroup: comp.lang.scheme

Nicolas Neuss wrote:

CL-USER> (defun fib (n)
(loop for x below n
for a = 0 then b
and b = 1 then (+ a b)
finally (return b)))
CL-USER> (mapcar #'fib (loop for x from 1 upto 20 collecting x))
(1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765)
CL-USER>

0-th Fibonacci is 0, IIRC. Furthermore, the use of loop's repeat clause is appropriate here. Thus,

(defun fib (n)
(loop repeat n
for a = 0 then b
and b = 1 then (+ a b)
finally (return a)))

"!" is similar to "do".

(define (fib n)
(! (b 1 (+ a b)
a 0 b
n n -)
(= 1 n)))

(! (n 1 +) (= n 7) ! print (fib n))

1
1
2
3
5
8

Given:

(define-syntax !-aux
(syntax-rules (<> @ + - cons cdr :in :across :if ! )
[(_ (:if bool z ...) (seen ... (v i u)) stuff ...)
(!-aux (z ...)
(seen ... (v i (if bool u v))) stuff ...) ]
;;
[(_ (x :in lst z ...) seen (lets ...) bool stuff ...)
(!-aux (x (and (pair? xs)(pop! xs)) <> z ...)
seen (lets ... (xs lst)) (or (not x) bool) stuff ...) ]
[(_ (x :across vec z ...) seen (lets ...) bool stuff ...)
(!-aux (x (and (< i (vector-length v))
(begin0 (vector-ref v i) (inc! i))) <>
z ...)
seen (lets ... (v vec) (i 0)) (or (not x) bool) stuff ...) ]
[(_ (a b <> z ...) (seen ...) stuff ...)
(!-aux (z ...) (seen ... (a b b)) stuff ...) ]
[(_ (a b + z ...) (seen ...) stuff ...)
(!-aux (z ...) (seen ... (a b (+ 1 a))) stuff ...) ]
[(_ (a + n z ...) (seen ...) stuff ...)
(!-aux (z ...) (seen ... (a 0 (+ n a))) stuff ...) ]
[(_ (a b - z ...) (seen ...) stuff ...)
(!-aux (z ...) (seen ... (a b (- a 1))) stuff ...) ]
[(_ (a cons b z ...) (seen ...) stuff ...)
(!-aux (z ...) (seen ... (a '() (cons b a))) stuff ...) ]
[(_ (a b cdr z ...) (seen ...) stuff ...)
(!-aux (z ...) (seen ... (a b (cdr a))) stuff ...) ]
[(_ (a b c z ...) (seen ...) stuff ...)
(!-aux (z ...) (seen ... (a b c)) stuff ...) ]
[(_ (a b) (seen ...) stuff ...)
(!-aux () (seen ... (a b)) stuff ...) ]
[(_ (a) (seen ...) stuff ...)
(!-aux () (seen ... (a '())) stuff ...) ]
;;
[(_ () seen lets bool ! action ...)
(!-aux () seen lets bool #t (action ...)) ]
;;
[(_ () ((a b c) z ...) lets bool)
(!-aux () ((a b c) z ...) lets bool a) ]
[(_ () ((a b c) z ...) lets bool @)
(!-aux () ((a b c) z ...) lets bool (reverse a)) ]
[(_ () seen lets bool @ result stuff ...)
(!-aux () seen lets bool (reverse result) stuff ...) ]
[(_ () seen lets bool (what @ x z ...) stuff ...)
(!-aux () seen lets bool (what (reverse x) z ...) stuff ...) ]
[(_ () seen lets bool (what x @ y z ...) stuff ...)
(!-aux () seen lets bool (what x (reverse y) z ...) stuff ...) ]
[(_ () ((a b c) z ...) lets 0 stuff ...)
(!-aux () ((a b c) z ...) lets (= 0 a) stuff ...) ]
[(_ () seen lets bool result stuff ...)
(let lets (do seen (bool result) stuff ...)) ]
))
(define-syntax !
(syntax-rules ()
[(_ specs bool stuff ...)
(!-aux specs () () bool stuff ...) ]
[(_ specs) (! specs #f) ]
))
--
[T]he problem is that lispniks are as cultish as any other devout group and basically fall down frothing at the mouth if they see [heterodoxy].
--- Kenny Tilton
The good news is, it's not Lisp that sucks, but Common Lisp. --- Paul Graham --- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: comp.lang.scheme

After a bit of effort, my first working lisp code which is slightly more complex than printing "hello", it returns the nth fibonacci number.
How would you lisp gurus have written the code in the proper lisp way.

(defun fib (n)
(let ( (f0 0) (f1 1) (counter 1) )
(loop
(if (>= counter n) (return-from fib f1) )
(let* ( (tmp f0) )
(setf f0 f1) (setf f1 (+ f1 tmp)) (incf counter)))))

Gauche Scheme

(define (nth-fib n)
(do ((n n (- n 1))
(a 0 b)
(b 1 (+ a b)))
((zero? n) b)))

(map nth-fib (iota 9))
===>
(1 1 2 3 5 8 13 21 34)
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