[perl #117935] [BUG] Sending named parameter ;p with value 0 to .postfix:<{ }> should yield the value and not the pair in Rakudo

[Carl Mäsak]

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<lizmat> rn: my %h= (:a<1>); say %h.postcircumfix:<{ }>("a", p => 0 )
<camelia> rakudo fe7049: OUTPUT«"a" => "1"␤»
<camelia> ..niecza v24-45-gbf8d2ad: OUTPUT«"a" => 1␤»
* lizmat thinks that is a bug, it should just be "1", not a pair
<masak> lizmat++ # finding all these nice corner cases
<masak> lizmat: want me to submit the p => 0 one?
<lizmat> masak: please
* masak submits lizmat's rakudobug

Usually, just accessing a hash yields "1" in the above case. The :p
parameter says "give me the pair", and so passing in :p (as a named
parameter or an adverb, same thing) should indeed give "'a' => '1'".
But here lizmat is passing the named parameter with the value 0 (one
of the falsy values in Perl 6), which should again turn it off. (Use
case: passing in a variable which may be truthy or falsy.)

[Carl Mäsak via RT]

<lizmat> actually, the :p(0) also applies to :delete and :exists
<lizmat> rn: my %a; %a<a>=1; say %a<a>:delete(0); say %a
<camelia> rakudo 2a04f2: OUTPUT«1␤().hash␤»
<camelia> ..niecza v24-50-gba63d9a: OUTPUT«1␤{}␤»
<jnthn> lizmat: Correct.
* masak adds that to the ticket

[Christian Bartolomaeus via RT]

There have been some relevant changes since this ticket was created:

1 postcircumfix:<{ }> is a sub now.

2 There was a change to the design documents and according to S02 the adverbial forms :p, :kv, :k, :v "weed out non-existing entries if the adverb is true; if not, they leave them in, just as an ordinary slice would" (cmp. https://github.com/perl6/specs/commit/fd94c28225).

Taking these changes into account, now the mentioned commands run as expected. First the :p(0) stuff:

$ perl6 -e 'my %h; %h<a>=1; say %h<a>:p'
"a" => 1

$ perl6 -e 'my %h; %h<a>=1; say %h<a>:p(0)' ## same result since key "a" exists
"a" => 1

$ perl6 -e 'my %h; %h<a>=1; say %h<a>:!p' ## same thing
"a" => 1

$ perl6 -e 'my %h; %h<a>=1; say %h<b>:p' ## key "b" does not exist

$ perl6 -e 'my %h; %h<a>=1; say %h<b>:p(0)' ## pair not weeded out
"b" => Any

$ perl6 -e 'my %h; %h<a>=1; say %h<b>:!p' ## same thing
"b" => Any

The adverbs :delete and :exists also work as designed:

$ perl6 -e 'my %h; %h<a>=1; say %h<a>:delete; say %h'
1


$ perl6 -e 'my %h; %h<a>=1; say %h<a>:delete(0); say %h'
1
"a" => 1

$ perl6 -e 'my %h; %h<a>=1; say %h<a>:exists'
True

$ perl6 -e 'my %h; %h<a>=1; say %h<a>:exists(0)'
False

For :p(0) I added tests to S32-hash/pairs.t with commit https://github.com/perl6/roast/commit/a543b07ab4

For :delete(0) and :exists(0) there are passing tests in S32-hash/delete-adverb.t and S32-exists-adverb.t, respectively.

I'm closing this ticket now.