Hi Linus! Although I just ported multiple usages of those kind of loops from a previously Racket project to a Guile project, I think this is quite cool! When I ported those usages in my code, it also resulted in some named lets (I guess quite naturally, as an available looping construct), so I can relate to that.
Thanks! Regards, Zelphir On 1/23/20 6:00 PM, guile-user-requ...@gnu.org wrote: > Message: 4 > Date: Thu, 23 Jan 2020 13:10:46 +0100 > From: Linus Björnstam <linus.inter...@fastmail.se> > To: guile-user@gnu.org > Subject: Announcing the first actually stable release of > guile-for-loops > Message-ID: <f536f849-5266-40d6-a3dc-f815834a0...@www.fastmail.com> > Content-Type: text/plain;charset=utf-8 > > 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
