Re: StackOverflowError in a specialized map

[Damien MATTEI <Damien dot Mattei at unice dot fr>]

Le Saturday 25 March 2017 23:56:01 Sudarshan S Chawathe, vous avez écrit :
> > From: Damien MATTEI <Damien.Mattei@unice.fr>
> > Date: Tue, 21 Mar 2017 15:00:57 +0100
> > 
> > yes, thank you, but i try to stay in a functional programming style
> > and avo= id "loop" that make code unreadable and hard to debug,
> 
> I suspect I may be misunderstanding your quest, but I don't see a
> significant difference between a 'named let' and a nested function
> definition (with respect to being functional programming).  Perhaps I
> should have used a name 'recur' instead of 'loop' in my earlier version.
> 
> For example, if we wish to avoid named let altogether for some reason,
> we could use the following variant of my earlier implementation.
> 
> (define (map/remove-nulls-1 proc . lsts)
>   (define (f lsts result)
>     (if (any null? lsts)
>         (reverse result)
>         (f (map cdr lsts)
>            (let ((proc-result (apply proc
>                                      (map car lsts))))
>              (if (null? proc-result)
>                  result
>                  (cons proc-result
>                        result))))))
>   (f lsts '()))
> 
> Or, going another way, we could use fold:
> 
> (define (map/remove-nulls-2 proc . lsts)
>   (reverse (apply fold
>                   (lambda fargs
>                     (let ((accum (last fargs))
>                           (pargs (drop-right fargs 1)))
>                       (let ((r (apply proc pargs)))
>                         (if (null? r)
>                             accum
>                             (cons r accum)))))
>                   '()
>                   lsts)))
> 
> As before, I'm using some SRFI 1 procedures for convenience; they can be
> avoided easily: any, fold, last, drop-right.  
> 
> Both the above versions, like the one I posted earlier, work without
> problems in Kawa without needing the --full-tailcalls option (i.e., Kawa
> properly detects and eliminates and simple cases of tail calls they
> use).  The slight awkwardness of last/drop-right is due to the
> 
> But, as I noted before, perhaps I'm missing the main point of the
> original question.
> 
> Regards,
> 
> -chaw
> 
> 
> 

i have tested your solution (just used some? in place of any):
;; (map/remove-nulls-1 (lambda (a b) (if (= a 2) '() (+ a b))) '(1 2 3) '(4 5 6)) -> '(5 9)
(define (map/remove-nulls-1 proc . lsts)
  (define (f lsts result)
    (if (some? #;any null? lsts)
        (reverse result)
        (f (map cdr lsts)
           (let ((proc-result (apply proc
                                     (map car lsts))))
             (if (null? proc-result)
                 result
                 (cons proc-result
                       result))))))
  (f lsts '()))

and it worked with Kawa without the need of --fulltail-calls option:
[mattei@moita ~]$ kawa
#|kawa:1|# (require 'regex)
#|kawa:2|# (include-relative  "../git/LOGIKI/lib/first-and-rest.scm")
/dev/stdin:2:20: cannot open file "../git/LOGIKI/lib/first-and-rest.scm"
#|kawa:3|# (exit)
[mattei@moita ~]$ cd Dropbox/Jkawa/
[mattei@moita Jkawa]$ kawa
#|kawa:1|# (require 'regex)
#|kawa:2|# (include-relative  "../git/LOGIKI/lib/first-and-rest.scm")
#|kawa:3|# (include-relative  "../git/LOGIKI/lib/syntactic-sugar.scm")
#|kawa:4|# (include-relative  "../git/LOGIKI/lib/display.scm")
#|kawa:5|# (include-relative  "../git/LOGIKI/lib/case.scm")
#|kawa:6|#
#|kawa:7|# (include-relative  "../git/LOGIKI/lib/list.scm")
#|kawa:8|# (include-relative  "../git/LOGIKI/lib/map.scm") ;; for map-nil*
/home/mattei/Dropbox/Jkawa/../git/LOGIKI/lib/map.scm:671:9: warning - no declaration seen for some?
#|kawa:9|# (include-relative  "../git/LOGIKI/lib/set.scm")
/home/mattei/Dropbox/Jkawa/../git/LOGIKI/lib/set.scm:131:3: warning - no declaration seen for andmap
#|kawa:10|#
#|kawa:11|# (define wds-url "http://ad.usno.navy.mil/wds/Webtextfiles/wdsnewref.txt";)
#|kawa:12|# (define wds-data-str &<{&[wds-url]})
#|kawa:13|# (define wds-data-str-split (regex-split (string #\linefeed) wds-data-str))
#|kawa:14|# (length wds-data-str-split)
22569
#|kawa:15|# (define test (map/remove-nulls-1 (lambda (x) x) wds-data-str-split))
#|kawa:16|# (length test)
22569

i think what prevent the optimisation to work in Kawa was the nesting of the recursion call in a let,
and the nesting of the tail call in a _cons_

Damien 

-- 
Damien.Mattei@unice.fr, Damien.Mattei@oca.eu, UNS / OCA / CNRS