Thank you so much for explaining what's going on here, Brad. You gave
a good example--just one that I misinterpreted. I think I understand
now: inside a regex Richard has to enclose his code within "<{ ... }>"
for it to be properly interpreted as a 'match objective' (I hope I
said that correctly).
mbook:~ homedir$ perl6
To exit type 'exit' or '^D'
> my @W = <perl weekly challenge with some extra things>;
[perl weekly challenge with some extra things]
> my $S = 'perlchallengeextrathingswithweeklysome' ; # randomly concatenate the
> words without spaces
perlchallengeextrathingswithweeklysome
> say $/ if $S ~~ / $<sol>=( { @W[3] } ) /;
｢｣
sol => ｢｣
> say $/ if $S ~~ / $<sol> = <{ @W[3] }> /;
｢with｣
sol => ｢with｣
> say $<sol>;
｢with｣
> my $sol = @W[3]; # with
with
> say $/ if $S ~~ / $<sol>=( $sol ) /;
｢with｣
sol => ｢with｣
> say $<sol>;
｢with｣
>
Also, I took the liberty of looking at your (Brad's) boolean code with
and without the :global adverb. I think it makes sense, however I do
see the REPL occasionally return "#<failed match>" when using the
:global adverb.
mbook:~ homedir$ perl6
To exit type 'exit' or '^D'
> say $/ if 'TrueFalse' ~~ m:g/ <{ Bool.pick }> /
()
> say $/ if 'TrueFalse' ~~ m:g/ <{ Bool.pick }> /
#<failed match>
> my @a = <True False>
[True False]
> say $/ if @a ~~ / <{ Bool.pick }> /
｢True｣
> say $/ if @a ~~ / <{ Bool.pick }> /
()
> say $/ if @a ~~ m:g/ <{ Bool.pick }> /
#<failed match>
> say $/ if @a ~~ m:g/ <{ Bool.pick }> /
()
>
Thanks, Bill.
On Sat, Jun 13, 2020 at 10:21 AM Brad Gilbert <b2gi...@gmail.com> wrote:
>
> That was just a dumb example.
> An incredibly dumb example.
>
> So what happens is that `Bool.pick` chooses The Bool values of either `True`
> or `False`.
> It does this at every position in the string.
>
> 'TrueFalse' ~~ / <{ Bool.pick }>
>
> Let's say that initially `Bool.pick` chooses `False`.
> That value then gets temporarily inserted into the regex.
> Obviously { "True" ne "False" } so it fails at the first position.
>
> So then the regex tries to match at the second position.
> `Bool.pick` gets run again, and picks one of the values.
> Neither "True" nor "False" can match here so it doesn't matter which is
> chosen.
>
> It keeps doing that until it finally matches or reaches the end of the string.
>
> Let's take a look at what happens at the fifth position.
> We obviously didn't match `True` at the start, because otherwise we would get
> this far.
> You may be expecting it to match `False` then.
> The only thing is that the code inside of <{ }> gets run again.
> This time it picks `True`.
> { "True" ne "False" } so it fails again.
>
> It then keeps trying to find a match, only we've gotten so far into the
> string that there are no matches left.
> So then it just fails.
>
> ---
>
> There is a 50% chance that it will return "True" if `Bool.pick` chooses
> `True` the first time.
> A 25% chance that it will return "False" if it picks `False` at the fifth
> position.
> And another 25% chance it will fail to match anything.
>
> You can play around with the odds by changing the string your matching
> against.
> There will always be a chance that it will fail to match though.
>
> On Sat, Jun 13, 2020 at 11:54 AM William Michels <w...@caa.columbia.edu>
> wrote:
>>
>> Hi,
>>
>> I seem to be having some problems with Brad's code. The 'boolean pick'
>> code seems far too clever for me to have intuited it on my own, so
>> (to expand my Raku/Perl6 vocabulary), I played around with matching
>> extra 'True' or 'False' values--as well as played around with seeing
>> if similar 'boolean elems' code would work. However the code (even
>> Brad's code) returned 'Nil' with alarming frequency (all code below
>> tested in the Raku/Perl6 REPL):
>>
>> mbook:~ homedir$ perl6
>> To exit type 'exit' or '^D'
>> > 'TrueFalse' ~~ / <{ Bool.pick }> /
>> ｢False｣
>> > 'FalseTrueFalse' ~~ / <{ Bool.pick }> /
>> ｢False｣
>> > 'TrueFalseTrue' ~~ / <{ Bool.pick }> /
>> Nil
>> > 'TrueFalseTrue' ~~ / <{ Bool.elems }> /
>> Nil
>> > 'TrueFalse' ~~ / <{ Bool.elems }> /
>> Nil
>> > 'TrueFalse' ~~ / <{ Bool.pick }> /
>> Nil
>> > 'TrueFalse' ~~ / <{ Bool }> /
>> Cannot resolve caller INTERPOLATE_ASSERTION(Match:D: Bool:U, BOOTInt,
>> BOOTInt, BOOTInt, BOOTInt, PseudoStash:D); none of these signatures
>> match:
>> (Match: Associative:D, $, $, $, $, $, *%_)
>> (Match: Iterable:D \var, int \im, int \monkey, int \s, $, \context, *%_)
>> (Match: Mu:D \var, int \im, int \monkey, $, $, \context, *%_)
>> in block <unit> at <unknown file> line 1
>>
>> > 'TrueFalse' ~~ / <{ Bool.say }> /
>> (Bool)
>> > say $*VM
>> moar (2020.02.1)
>> > exit
>> mbook:~ homedir$ perl6 --version
>> This is Rakudo version 2020.02.1.0000.1 built on MoarVM version 2020.02.1
>> implementing Raku 6.d.
>> mbook:~ homedir$
>>
>> Any help appreciated, Bill.
>>
>>
>> On Sat, Jun 13, 2020 at 6:42 AM Brad Gilbert <b2gi...@gmail.com> wrote:
>> >
>> > Inside of a regex `{…}` will just run some regular Raku code.
>> > Code inside of it will most likely have no effect on what the regex
>> > matches.
>> >
>> > What you should have written was:
>> >
>> > $<sol> = "@W[3]"
>> >
>> > The thing you were thinking of was:
>> >
>> > $<sol> = <{ @W[3] }>
>> >
>> > Which could have been written as:
>> >
>> > <sol={ @W[3] }>
>> >
>> > ---
>> >
>> > To have the result of regular Raku code have an effect on the match, it
>> > has to have <…> around it
>> >
>> > 'TrueFalse' ~~ / <{ Bool.pick }> /
>> >
>> > I think it is better if you use "…" if you are just interpolating a
>> > variable, because that is something you might do outside of a regex as
>> > well.
>> >
>> > ---
>> >
>> > The reason your code matched is that an empty regex always matches.
>> >
>> > 'abc' ~~ / "" /
>> > 'abc' ~~ / {} /
>> > 'abc' ~~ / {'def'} / # still an empty regex as far as the regex engine
>> > is concerned
>> >
>> > On Sat, Jun 13, 2020 at 5:35 AM Richard Hainsworth
>> > <rnhainswo...@gmail.com> wrote:
>> >>
>> >> I was playing with a regex and array interpolation.
>> >>
>> >> From the documentation I thought the following comparisons would be the
>> >> same, but they are not.
>> >>
>> >> What am I missing?
>> >>
>> >> my @W = <perl weekly challenge with some extra things>;
>> >> my $S = 'perlchallengeextrathingswithweeklysome' ; # randomly concatenate
>> >> the words without spaces
>> >> say 'yes' if $S ~~ / $<sol>=( { @W[3] } ) /;
>> >> say $<sol>;
>> >> my $sol = @W[3]; # with
>> >> say 'yes' if $S ~~ / $<sol>=( $sol ) /;
>> >> say $<sol>;
>> >>
>> >> <response>
>> >> yes
>> >> ｢｣
>> >> yes
>> >> ｢with｣
>> >>
>> >>
>> >>
