See Challenge #2 in https://theweeklychallenge.org/blog/perl-weekly-challenge-131/ ... !
-y On Wed, Aug 25, 2021 at 2:08 PM William Michels <w...@caa.columbia.edu> wrote: > Hi Andy! > > Maybe this helps (separate coding elements with parens and/or brackets, > still get the same result): > > > say 1, 1, * + * ...^ *>= 100; > (1 1 2 3 5 8 13 21 34 55 89) > > > say 1, 1, * + * ...^ (*>= 100); > (1 1 2 3 5 8 13 21 34 55 89) > > > say 1, 1, * + * ...^ ( * >= 100); > (1 1 2 3 5 8 13 21 34 55 89) > > > say (1, 1, * + *) ...^ ( * >= 100); > (1 1 2 3 5 8 13 21 34 55 89) > > > say 1, 1, * + * [...^] ( * >= 100); > (1 1 2 3 5 8 13 21 34 55 89) > > > say (1, 1, * + *) [...^] ( * >= 100); > (1 1 2 3 5 8 13 21 34 55 89) > > From Yary: > >> Ranges also support arbitrary functions, the doc page shows a Fibonacci > number generator > >> https://docs.raku.org/language/operators#index-entry-sequence_operator > > The Fibonacci code above (and in the docs) uses the sequence operator > (infix ...), not the range operator (infix ..). To recap for Andy: Yary, > Vadim, Brian, Fernando and Marc have posted code using the sequence > operator; I've previously posted code using the range operator coupled with > a grep() call [I recall reading somewhere that ranges are cheaper to > construct than sequences, but can't locate the reference at the moment]. > > FWIW_1, I was unable to get the Fibonacci code to work with the range > operator: > > > say 1, 1, * + * ..^ *>= 100; > 11WhateverCode.new > > FWIW_2, I've had good luck grepping out composite sequences with the > 'range_operator / grep' strategy: > > > #Using "(^*)" as a synonym for the range "(0..*-1)", see: > https://docs.raku.org/type/Range > Nil > > > ( 0..11 ).[ (^*).grep: * %% 2 ] > (0 2 4 6 8 10) > > > ( 0..11 ).[ (^*).grep: * %% 3 ] > (0 3 6 9) > > > ( 0..11 ).[ (^*).grep: * %% (2|3) ] > (0 2 3 4 6 8 9 10) > > > ( 0..11 ).[ (^*).grep: * %% any(2,3) ] > (0 2 3 4 6 8 9 10) > > HTH, Bill. > > PS Now to try to understand the differences (shown earlier in this thread) > when the := binding operator is used! > > > On Wed, Aug 25, 2021 at 7:15 AM Andy Bach <andy_b...@wiwb.uscourts.gov> > wrote: > >> I "misread" >> say 1, 1, * + * ...^ *>= 100; >> >> thinking "shouldn't it be '<=' as you want the total to be less than >> 100?" but >> $ raku -e 'say 1, 1, * + * ...^ *<= 100;' >> ===SORRY!=== Error while compiling -e >> Whitespace required before <= operator >> at -e:1 >> ------> say 1, 1, * + * ...^ *<= 100;⏏<EOL> >> expecting any of: >> postfix >> >> and >> $ raku -e 'say 1, 1, * + * ...^ * <= 100;' >> () >> $ raku -e 'say 1, 1, * + * ...^ * >= 100;' >> (1 1 2 3 5 8 13 21 34 55 89) >> >> So, then it dawned on me that the '>=' is "binding" (right word?) to the >> "*" marking the end of the sequence as "until I am ge 100". Though that >> doesn't quite work, >> $ raku -e 'say 1, 1, * + * ...^ * <= 100;' >> () >> >> Ah, I see, it does work. The end of the sequence is the first number less >> than 100, so 1 succeeds. I guess the sequence never gets started. >> ------------------------------ >> *From:* yary <not....@gmail.com> >> *Sent:* Tuesday, August 24, 2021 8:39 PM >> *To:* William Michels <w...@caa.columbia.edu> >> *Cc:* Marc Chantreux <e...@phear.org>; raku-users <perl6-users@perl.org> >> *Subject:* Re: [better solution] pairs of separators from a string >> >> >> *CAUTION - EXTERNAL: * >> Hi Bill, >> >> When building a range that's an arithmetic or geometric progression, the >> sequence operator is a little quicker to type. And thus also more likely to >> be understood more quickly too. >> >> > ('a' .. 'h')[(0..*-1).grep: * %% 2 ] >> (a c e g) >> > ('a' .. 'h')[ 0, 2 ... * ] >> (a c e g) >> >> > ('a' .. 'h')[(0..*-1).grep: * % 2 ] >> (b d f h) >> > ('a' .. 'h')[1, 3...*] >> (b d f h) >> >> # Geometric example- powers of 2 >> > ('a' .. 'z')[1, 2, 4...*] >> (b c e i q) >> >> There isn't a simple translation for the is-prime example that I can >> think of, that is a good use for "grep" >> >> Ranges also support arbitrary functions, the doc page shows a Fibonacci >> number generator >> https://docs.raku.org/language/operators#index-entry-sequence_operator >> "This allows you to write >> >> say 1, 1, * + * ...^ *>= 100; >> # OUTPUT: «(1 1 2 3 5 8 13 21 34 55 89)» >> >> to generate all Fibonacci numbers up to but excluding 100." >> >> >> >> -y >> >> >> On Tue, Aug 24, 2021 at 6:36 PM William Michels via perl6-users < >> perl6-users@perl.org> wrote: >> >> Hi Marc, >> >> My understanding is that ranges are pretty cheap to construct, and in any >> case, the range @x[0..*-1] is just the index of all elements in @x. The >> .grep() approach may be most useful if you have a function (e.g. %, %%, and >> .is-prime shown below): >> >> > (0...9) >> (0 1 2 3 4 5 6 7 8 9) >> > (0...9)[0..*-1] >> (0 1 2 3 4 5 6 7 8 9) >> > (0...9)[(0..*-1).grep: * ] >> (0 1 2 3 4 5 6 7 8 9) >> > (0...9)[(0..*-1).grep: * %% 2 ] >> (0 2 4 6 8) >> > (0...9)[(0..*-1).grep: * % 2 ] >> (1 3 5 7 9) >> > (0...9)[(0..*-1).grep: *.is-prime ] >> (2 3 5 7) >> > >> >> You can find a related example in the docs ( >> https://docs.raku.org/routine/grep#class_HyperSeq). Anyway, I'm sure >> each approach has its fans, >> >> Best, Bill. >> >> On Tue, Aug 24, 2021 at 3:59 AM Marc Chantreux <e...@phear.org> wrote: >> >> hello everyone, >> >> I made a mistake while replying to all of us so anwsers never reached >> your boxes. I'll summerize in one answer: >> >> Bill: >> >> > Is it just even/odd elements that you want to separate out? If so, maybe >> > .grep() is your friend here >> >> I don't think it is: 0, 2 ... * seems to be >> >> * closer to what i have in mind when i think about the problem >> (so i invoke readability there) >> * probably more efficient than (0..*).grep(* % 2) that >> * generate twice the number of required elements >> * need to filter the result >> >> Also, trying to play with this version: >> >> my ($a,$b) = >> .[0,2...*], >> .[1,3...*] >> with <AaBbCc>.comb; >> >> just don't work because the lists are squashed into scalar context >> in the process. >> >> So Brian and Fernando made my day with := and the unexpected power of >> the [] operator. >> >> my (@a,@b) := <AaBbCc>.comb[ [0,2...*], [1,3...*] ]; >> >> I really like how declarative it is. Also the use of := now seems >> obvious to me. >> >> Sigils still remains something strange to me desprite all your examples >> but i'll take some time. thanks everyone. >> >> marc >> >> *CAUTION - EXTERNAL EMAIL:* This email originated outside the Judiciary. >> Exercise caution when opening attachments or clicking on links. >> >
