---------- 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 > >
