Re: Ex. 3.5 in ACL

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 ...) ] ))