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 >> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
