From Newsgroup: comp.lang.lisp

Zachary Beane wrote:

I am just trying to solve Ex 3.5 in Graham's ANSI Common Lisp book. I am reading it on my own and not as part of a university course. The task is:

define a function pos+, that takes a list as param and returns a list
that adds the position of each element of the list to the element's value. Thus:
(pos+ '(7 5 1 4))
returns:
(7 6 3 7)

...but it's also easy with DO:

(defun do-pos+ (orig-list)
(do ((i 0 (1+ i))
(list orig-list (cdr list))
(new-list nil (cons (+ (car list) i) new-list)))
((endp list) (nreverse new-list))))

(define (do-pos+ orig-list)
(do_ ((i 0 (+ 1 i))
(x :in orig-list)
(result :collect (+ i x)))
(#f @ result)))

(do-pos+ '(200 300 400))
===>
(200 301 402)

Given:

(define-syntax do_-aux
(syntax-rules ( <> @ :in :collect )
[ (do_-aux ((x what <>) more ...) (seen ...) stuff ...)
(do_-aux (more ...) (seen ... (x what what)) stuff ...) ]
[ (do_-aux ((x :in seq) more ...) seen (lets ...) (bool z ...) stuff ...)
(do_-aux ((x (and (pair? the-list) (car the-list)) <>) more ...)
seen
(lets ... (the-list seq))
((or (null? the-list) (begin (pop! the-list) #f) bool) z ...)
stuff ...) ]
[ (do_-aux ((accum :collect x) more ...) stuff ...)
(do_-aux ((accum '() (cons x accum)) more ...) stuff ...) ]
[ (do_-aux (spec more ...) (seen ...) stuff ...)
(do_-aux (more ...) (seen ... spec) stuff ...) ]
[ (do_-aux () seen lets (bool y ... @ result) stuff ...)
(do_-aux () seen lets (bool y ... (reverse result)) stuff ...) ]
[ (do_-aux () seen (lets ...) more ...)
(let (lets ...)
(do seen more ...))
] ))
(define-syntax do_
(syntax-rules ()
[ (do_ specs more ...)
(do_-aux specs () () more ...) ] ))
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: comp.lang.lisp

B. Pym wrote:

(defun mapcar-pos+ (list)
(let ((i -1))
(mapcar #'(lambda (elt) (+ elt (incf i)))

iteration:

(defun pos+ (lst)
(setf acc NIL)
(setf i 0)
(dolist (obj lst)
; i know, instead of append, i could do a cons and reverse afterwards...
(progn (setf acc (append acc (list (+ obj i))))
(setf i (+ i 1))))
acc)

I'd prefer LOOP here:

(defun loop-pos+ (list)
(loop for i from 0
for elt in list
collect (+ elt i)))

(defun pos+ (xs)
(do ((i 0 (+ 1 i))
r)
((not xs) (reverse r))
(push (+ i (pop xs)) r)))
--
[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.lisp

B. Pym wrote:

B. Pym wrote:

(defun mapcar-pos+ (list)
(let ((i -1))
(mapcar #'(lambda (elt) (+ elt (incf i)))

iteration:

(defun pos+ (lst)
(setf acc NIL)
(setf i 0)
(dolist (obj lst)
; i know, instead of append, i could do a cons and reverse afterwards...
(progn (setf acc (append acc (list (+ obj i))))
(setf i (+ i 1))))
acc)

I'd prefer LOOP here:

(defun loop-pos+ (list)
(loop for i from 0
for elt in list
collect (+ elt i)))

(defun pos+ (xs)
(do ((i 0 (+ 1 i))
r)
((not xs) (reverse r))
(push (+ i (pop xs)) r)))

(define (pos+ xs)
(Do ((i 0 (+ 1 i))
r)
((null? xs) @ r)
(push! r (+ i (pop! xs)))))

Given:

(define-syntax Do-aux
(syntax-rules (<> @ values)
[(_ ((a b <>) d ...) (seen ...) z ...)
(Do-aux (d ...) (seen ... (a b b)) z ...) ]
[(_ ((a b c ...) d ...) (seen ...) z ...)
(Do-aux (d ...) (seen ... (a b c ...)) z ...) ]
[(_ ((a) d ...) (seen ...) z ...)
(Do-aux (d ...) (seen ... (a '())) z ...) ]
[(_ (a d ...) (seen ...) z ...)
(Do-aux (d ...) (seen ... (a '())) z ...) ]
[(_ () seen (a b ... @ (values x ...)) z ...)
(Do-aux () seen (a b ... (values (reverse~ x) ...)) z ...) ]
[(_ () seen (a b ... @ xs) z ...)
(Do-aux () seen (a b ... (reverse xs)) z ...) ]
[(_ () seen till body ...)
(do seen till body ...) ]))
(define-syntax Do
(syntax-rules ()
[(_ specs till body ...)
(Do-aux specs () till body ...) ]))
--
[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