On Fri, 24 Jan 2020, at 09:16, Arne Babenhauserheide wrote: > Hi, > > Linus Björnstam <linus.inter...@fastmail.se> writes: > > 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. > > That’s cool! > > > (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 > > Is there a chance that this could get included in Guile (ice-9 > for-loops?) and become a SRFI?
John Cowan asked me to write a SRFI, but right now I don't think it is really in good enough shape to be a srfi. The for/foldr internals is a can of worms. Currently I am planning on removing the "procedural" part of that (stolen from what I saw in the macro expansion of racket's for/foldr) and resort to macros generating macros instead (due to otherwise losing syntax context information). I could probably trim at least 100 lines of code from the implementation as it is now. > > If the code is non-portable (I guess the #:keywords are), the two > existing implementations (Racket, Guile) would still be sufficient for a > SRFI. The code is surprisingly portable as long as you are porting to a syntax-case scheme! Redefining the keywords as auxiliary syntax made porting an earlier version to chez scheme a 2 evening job :) I still had some annoying bugs that I didn't want to spend time on, but it shouldn't be hard. Some of the recent changes to the code was introduced to facilitate porting to non-keyword schemes: (in-range a b #:incr c) => (in-range/incr a b c), for example. The only downside is that I would have to squat on when:, unless:, final:, break:, length: and fill:. /Linus
