Hello Timo, and thank you for taking the time to explain how "comb"
routine signatures work. I have no doubt your description is the
correct way to use comb routine(s) in Raku/Perl6.
First of all, I should preface my remarks by saying that I'm using
Rakudo (moar) 2019.07.1, with the Linenoise module to run the
Raku/Perl6 REPL. It has been suggested to me that my install might
somehow be broken, because I tried to 'roll-my-own' Rakudo-Star
release (basically I copied over pre-installed modules from my Rakudo
2019.03 install, and ran 'zef update').
In any case, I haven't been able to get the code you posted to work. I
checked all six examples in the REPL, and the last example I checked
at the command line as well. I'm hoping someone on the list running
Rakudo (moar) 2019.07.1 can confirm/refute my results:
> #Timo
Nil
> comb(/\w/, "a;b;c", match => True);
Unexpected named argument 'match' passed
in block <unit> at <unknown file> line 1
> comb(/\w/, "a;b;c", :match);
Unexpected named argument 'match' passed
in block <unit> at <unknown file> line 1
> comb(/\w/, "a;b;c", :match(True));
Unexpected named argument 'match' passed
in block <unit> at <unknown file> line 1
> comb(/\w/, "a;b;c", :!match);
Unexpected named argument 'match' passed
in block <unit> at <unknown file> line 1
> comb(/\w/, "a;b;c", :match(False));
Unexpected named argument 'match' passed
in block <unit> at <unknown file> line 1
> comb(/\w/, "a;b;c", 2, :match);
Unexpected named argument 'match' passed
in block <unit> at <unknown file> line 1
> $*VM
moar (2019.07.1)
>
> exit
mbook:~ homedir$ perl6 -e 'comb(/\w/, "a;b;c", 2, :match);'
Unexpected named argument 'match' passed
in block <unit> at -e line 1
mbook:~ homedir$
As for what's going on, I'm wondering if there might be an issue with
"comb" signatures in general. There exists both a '(Str) routine comb'
and a '(Cool) routine comb'. Maybe these two routines are somehow
interfering with each other?
Thank you, and any further help appreciated, Bill.
On Sat, Nov 16, 2019 at 6:34 AM Timo Paulssen <t...@wakelift.de> wrote:
>
> Hi Bill,
>
> In your repl examples you're actually passing the True or False as a
> positional parameter, which makes it go into the slot for $limit, not the
> slot for :$match.
>
> In order to pass true or false for the "match" named parameter you have
> different syntactical options:
>
> comb(/\w/, "a;b;c", match => True) # maybe the simplest is using a pair
>
> comb(/\w/, "a;b;c", :match) # using "colon pair" syntax; it's syntax that
> puts a colon at the beginning and makes a pair
>
> comb(/\w/, "a;b;c", :match(True)) # :match is short for match => True, and
> :match(True) is long for match => True
>
> comb(/\w/, "a;b;c", :!match) # putting a ! after the : negates the pair,
> i.e. it's now match => False
>
> comb(/\w/, "a;b;c", :match(False)) # same value
>
> And on top of that, you can add the third positional parameter to pass a
> value for $limit
>
> comb(/\w/, "a;b;c", 2, :match) # output up to two results, as match objects
>
> Here's a few comments on the examples you pasted:
>
>
> > On another note (or possibly the same note), I tried code similar to >
> > Joe's with fair success. I was able to get the REPL to understand a >
> > "True" or "False" parameter, but never in conjunction with a > "$limit"
> > parameter. Is this the correct behaviour, and why?
> The surprise here comes from Bool actually being derived from Int, and
> therefore being totally acceptable values to pass for $limit.
> >> #REPL > Nil >> say comb(/\w/, "a;b;c", False).perl; > ().Seq You can see
> >> here that it gave no results; that's because it interpreted the False as 0
> >> in the $limit parameter.
>
> >> say comb(/\w/, "a;b;c", True).perl; > ("a",).Seq
> Here the True is interpreted as 1 for $limit, giving you just "a", and it's a
> string because the match named parameter wasn't given and defaulted to False.
> >> say comb(/\w+/, "a;b;c", True).perl; > ("a",).Seq
> The difference between \w and \w+ isn't noticeable here, as the source string
> only ever has single word character in a row, but you can try with "ab;cd;ef"
> for example with both \w and \w+.
>
> >> say comb(/\w+/, "a;b;c", 2).perl; > ("a", "b").Seq >> say comb(/\w+/,
> >> "a;b;c", 3).perl; > ("a", "b", "c").Seq >> say comb(/\w+/, "a;b;c",
> >> 4).perl; > ("a", "b", "c").Seq >> say comb(/\w+/, "a;b;c", True).perl; >
> >> ("a",).Seq
> Same as above; True being interpreted as 1
>
> >> say comb(/\w+/, "a;b;c", 2, True).perl; > Too many positionals passed;
> >> expected 2 or 3 arguments but got 4 in > block <unit> at <unknown file>
> >> line 1
> There's no syntax here that distinguishes 2, a positional parameter, from
> True, also a positional parameter.
>
> >> say comb(/\w+/, "a;b;c", 2, :True).perl; > Unexpected named argument
> >> 'True' passed in block <unit> at <unknown > file> line 1
> The issue here is that :True is short for True => True, i.e. passing the
> value True to the named parameter called "True", easy to get confused by the
> error message here!
> > Any help appreciated, Bill.
>
> I hope the explanations make sense!
> - Timo
