Yeah, when iterating through many different things at the same time it is extremely helpful.
I would have loved syntax parse when writing the macros :) I read your for loops code in awe, at least until I saw how you "cheated" with set! :-P My only chance of getting it into guile proper would be to 1. Make a SRFI and survive the SRFI process with my honour intact and 2. Code cleanup. Most of for/emit is OKish, but for/foldr needs to be beaten with a stick, burnt and rewritten. "bending hygiene" doesn't quite cover what I did to make it work. In the end I sort of kind of worked around it by making an API change, but it still stinks. Defining a new loop using for/foldr involves having to do a syntax->datum->syntax. No fun. I could check how racket does it, but given they can do syntax-local-introduce (which is specific to their "hygiene as sets of scopes") I suspect I am out of luck. Väl mött Linus Björnstam On Fri, 24 Jan 2020, at 13:13, Stefan Israelsson Tampe 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 > > <https://man.sr.ht/~bjoli/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 > >