+1 On Fri, Jan 24, 2020, 20:13 Stefan Israelsson Tampe <stefan.ita...@gmail.com> wrote:
> > > ---------- Forwarded message --------- > From: Stefan Israelsson Tampe <stefan.ita...@gmail.com> > Date: Fri, Jan 24, 2020 at 12:42 PM > Subject: Re: Announcing the first stable release of guile-for-loops > To: Linus Björnstam <linus.bjorns...@veryfast.biz> > > > Would be cool to have those implemented in guile, that would make my > guile-syntax-parse a bit leaner > > Regards > Stefan > > On Thu, Jan 23, 2020 at 3:03 PM Linus Björnstam < > linus.bjorns...@veryfast.biz> wrote: > >> Hiya everybody! >> >> I have spent some time implementing efficient for loops for guile, and >> they are baked and ready to go. I have worked the last weeks at >> implementing generalized support for non-tail-recursive loops and am happy >> to announce for/foldr. It is a generic right fold, with support for >> delaying it's arguments as either thunks or promises. >> >> The syntax is more or less the same as racket's loops, and they are >> generally compatible. The code generated is for almost all cases as fast as >> hand-rolled code. They are all expressed as left or right folds, and are as >> such (apart from for/list, but read about that in the documentation) free >> of mutation. They are all converted to named lets. >> >> Some examples: >> >> (for/list ((a (in-range 1 6))) >> (* a a)) ;; => (1 4 9 16 25) >> >> (for*/list ((a (in-string "ab")) (b (in-range 1 3))) >> (list a b)) >> ;; => ((#\a 1) (#\a 2) (#\b 1) (#\b 2)) >> >> There are many more looping constructs, among others: >> for/sum, for/vector, for/or, for/and, for/first, for/last and a >> side-effecting simple for. >> >> Here is a sieve of erathostenes: >> >> (define (erathostenes n) >> (define vec (make-vector n #t)) >> (for/list ([i (in-range 2 n)] #:when (vector-ref vec i)) >> (for ([j (in-range/incr (* 2 i) n i)]) >> (vector-set! vec j #f)) >> i)) >> >> The code and documentation is available here: >> https://hg.sr.ht/~bjoli/guile-for-loops >> >> A web-friendly documentation can be found here: >> https://man.sr.ht/%7Ebjoli/for-loops-docs/for-loops.md >> >> The thing I had been waiting for is right fold. That allows us to write >> loops like guile's map: non-tail recursive: >> (for/foldr ((identity '())) ((a (in-list '(1 2 3)))) >> (cons (* a a) identity)) >> >> becomes equivalent to: >> >> (let loop ((random-identifier '(1 2 3))) >> (if (null? random-identifier) >> '() >> (let ((a (car random-identifier))) >> (cons (* a a) (loop (cdr random-identifier)))))) >> >> Happy hacking >> Linus Björnstam >> >>
