Apologies, looks like the smartmatch operator is listed in the Operator Precedence table (15th row: under "Chaining infix"):
https://docs.raku.org/language/operators#Assignment_operators However, am I correct in stating that the assignment operator ("=") is on the 19th row ("Item assignment")? Therefore in the absence of parentheses, etc., all smartmatch operations take precedence over assignment operations? Best Regards, Bill. On Sat, Dec 7, 2019 at 10:27 PM William Michels <w...@caa.columbia.edu> wrote: > > Wow Brad, that's interesting and informative. > > I haven't seen the S/// operator before, so I had to look it up. On > the first page I found the docs say (quite informatively): "S/// uses > the same semantics as the s/// operator, except it leaves the original > string intact and returns the resultant string instead of $/ ($/ still > being set to the same values as with s///)." > > https://docs.raku.org/syntax/S$SOLIDUS$SOLIDUS$SOLIDUS > > I was then able to find an overview on regexes, which more explicitly > names the "S///" operator as "Non-disruptive substitution". I suppose > I could quibble and request that the phrase "Non-disruptive > substitution" be added to the operator page (above), but no > matter--it's easy enough to find: > > https://docs.raku.org/language/regexes#S///_non-destructive_substitution > > So I think I understand that (as Brad has said): "smartmatch with S/// > (or TR///) is not useful." Conversely, I've also found another > smartmatch construct that is useless (i.e. disallowed): > > > my $r = 'abc' ~~ { S/b/./ } > a.c > > my $s = 'abc' ~~ { s/b/./ } > Cannot modify an immutable Str (abc) > in block <unit> at <unknown file> line 1 > > > > No matter how "discouraged' a particular syntax is, people are going > to run into these disallowed syntaxes and wonder why. Could it be due > to precedence? These two prohibited operations beg the question: can a > definitive statement be made regarding the precedence of the > smartmatch operator relative to either lowercase-triple-solidus > operators such as s/// and tr/// , or relative to > uppercase-triple-solidus operators such as S/// and TR/// ? > > This really makes me wonder if anyone has plans to add "~~" (the > smartmatch operator) to the precedence table that can be found > below--and where in the table the smartmatch operator would precisely > sit: > > https://docs.raku.org/language/operators#Operator_precedence > > Best Regards, Bill. > > > > > On Sat, Dec 7, 2019 at 7:53 AM Brad Gilbert <b2gi...@gmail.com> wrote: > > > > The return value of s/// is the same as $/ > > > > If you want the resulting string instead you can use S/// instead. > > > > > $_ = 'abc' > > > my $r = S/b/./ > > > say $r > > a.c > > > > Note that it warns you try to use S/// with ~~ > > > > > my $r = 'abc' ~~ S/b/./ > > Potential difficulties: > > Smartmatch with S/// is not useful. You can use given instead: S/// > > given $foo > > ------> my $r = 'abc' ~~ S/b/./ > > False > > > > Which gives you an indicator of how to fix it > > > > > my $r = S/b/./ given 'abc' > > a.c > > > > Note that the `given` happens before the `=` > > > > So it works the same as > > > > > my $r = ( S/b/./ given 'abc' ) > > a.c > > > > --- > > > > The reason ~~ doesn't work with S/// has to do with the dual pass nature of > > ~~. > > > > Without getting into details, you can avoid that by delaying the S/// until > > the second pass. > > > > > my $r = 'abc' ~~ { S/b/./ } > > a.c > > > > Or you can just set $_ to the value. > > (Which is basically what the previous line is doing.) > > > > > my $r = S/b/./ given 'abc' > > > > > given 'abc' { > > > my $r = S/b/./ > > > … > > > } > > > > > my $_ = 'abc' > > > my $r = S/b/./ > > > > > my $r = 'abc' ~~ -> $_ { S/b/./ } > > > > > my $r = 'abc' ~~ sub ( $_ ) { S/b/./ } > > > > > my $r = 'abc' ~~ anon sub foo ( $_ ) { S/b/./ } > > --- > > > > One of design goals of Raku is to have as few special cases as possible. > > Which is why ~~ and S/// haven't been made to just work. > > > > (It could be argued that in this case an exception could be made. But I'm > > not going to argue for it.) > > > > On Fri, Dec 6, 2019 at 10:37 PM William Michels via perl6-users > > <perl6-us...@perl.org> wrote: > >> > >> Hello All, > >> > >> Todd put up some interesting code yesterday using the Raku/Perl6 REPL, > >> which I reproduced with no problem. Additionally I tried some > >> variations removing and/or moving parentheses to a different location, > >> and have numbered the relevant REPL lines 1 through 6: > >> > >> mbook:~ homedir$ perl6 > >> To exit type 'exit' or '^D' > >> 1> my $x = Q[word</b><br>] ; > >> word</b><br> > >> 2> (my $y = $x) ~~ s/ '<' .* //; say $/; say $x; say $y; > >> ｢</b><br>｣ > >> word</b><br> > >> word > >> 3> my $a = Q[word</b><br>] ; > >> word</b><br> > >> 4> my $b = ($a ~~ s/ '<' .* //); say $/; say $a; say $b; > >> ｢</b><br>｣ > >> word > >> ｢</b><br>｣ > >> > my $c = Q[word</b><br>] ; > >> word</b><br> > >> > my $d = $c ~~ s/ '<' .* //; say $/; say $c; say $d; > >> ｢</b><br>｣ > >> word > >> ｢</b><br>｣ > >> 7> $*VM > >> moar (2019.07.1) > >> > >> Working in groups of 2, lines 1 and 2 replicate the code Todd put up > >> (parenthesis surrounding everything to the left of the smartmatch > >> operator). I get the same result as Todd. What interests me are lines > >> 3 through 6. Lines 3 and 4 are the virtually the same code but with > >> parentheses surrounding everything to the right hand side (RHS) of the > >> assignment operator (" = "). As people will note, lines 2 and lines 4 > >> give different results. Removing parentheses entirely in line 6 gives > >> the same result as in line 4. Because the results in line 4 and line 6 > >> are the same, this says that as far as parentheses are concerned, the > >> smartmatch operator "~~" takes precedence over the assignment operator > >> "=". > >> > >> What's not clear to me in the code above (lines 4 and 6) is why > >> variables $b and $d get assigned to $/. I would have expected in line > >> 4 that $a would have been matched against the smartmatch, and the > >> result ("word") would have been simply copied into variable $b. Have I > >> misunderstood? > >> > >> Anyway, I'm just hoping to start a conversation on the topic of > >> precedence in general, and hopefully getting some feedback as to where > >> to look in the docs for further instruction. > >> > >> Best Regards, Bill. > >> > >> > >> On Fri, Dec 6, 2019 at 12:15 AM ToddAndMargo via perl6-users > >> <perl6-us...@perl.org> wrote: > >> > > >> > On 2019-12-05 23:19, ToddAndMargo via perl6-users wrote: > >> > > On 2019-12-05 03:09, William Michels via perl6-users wrote: > >> > >> What happens when you type "perl6" or "raku" at the bash command > >> > >> prompt? > >> > > > >> > > Hi William, > >> > > > >> > > On my shop machine, it jumps to the next line with an > >> > > empty flashing cursor > >> > > > >> > > On my office machine, it told me to install > >> > > zef install Readline > >> > > > >> > > After that, I get: > >> > > > >> > > $ perl6 > >> > > To exit type 'exit' or '^D' > >> > > > > >> > > > >> > > and > >> > > > >> > > > say "hello World" > >> > > hello World > >> > > > say "B" ~ Q[:\] ~ " drive dismounted" > >> > > B:\ drive dismounted > >> > > > > >> > > > >> > > and sticking an obvious booboo into it > >> > > > >> > > > if 3 % 2 = 1 {say "odd"}; > >> > > Cannot modify an immutable Int (1) > >> > > in block <unit> at <unknown file> line 1 > >> > > > >> > > Plus I can use the arrow keys to recall previous lines too. > >> > > > >> > > Time up update my Perl6 on my shop computer! > >> > > > >> > > No more hassling with `perl6 -e` !!! > >> > > > >> > > Dude! THANK YOU !!!!!! > >> > > > >> > > -T > >> > > >> > You've created a monster!! > >> > > >> > perl6 > >> > To exit type 'exit' or '^D' > >> > > my $x = Q[</b><br>] > >> > </b><br> > >> > > say $x > >> > </b><br> > >> > > (my $y = $x ) ~~ s/ Q[<] .* //; > >> > ===SORRY!=== Error while compiling: > >> > Unrecognized regex metacharacter < (must be quoted to match literally) > >> > ------> (my $y = $x ) ~~ s/ Q[<] .* //; > >> > > my $x = Q[abc</b><br>] > >> > abc</b><br> > >> > > (my $y = $x ) ~~ s/ '<' .* //; > >> > ｢</b><br>｣ > >> > > (my $y = $x ) ~~ s/ '<' .* //; say $y > >> > abc > >> > > (my $y = $x ) ~~ s/ '<' .* //; say $x; say $y > >> > abc</b><br> > >> > abc > >> > > >> > > >> > Thank you! > >> > > >> > > >> > -- > >> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >> > Computers are like air conditioners. > >> > They malfunction when you open windows > >> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
