Re: StackOverflowError in a specialized map

[Damien MATTEI <Damien.Mattei@unice.fr>]

i removed the nested _let_ ,the only thing that make crash the stack are the _cons_ that grow at each recursive call 
for some explanation see:
https://mitpress.mit.edu/sicp/full-text/book/book-Z-H-11.html#%_sec_1.2.1

Damien
Le Tuesday 28 March 2017 10:42:25 Damien MATTEI, vous avez écrit :
> 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