leszekdubiel has asked for the wisdom of the Perl Monks concerning the following question:

I decided to give a try to perl6 and I got stuck -- how to parse date in format %Y-%m? Year and month only...? 
perl6 -e  'say Date.new("2019-01-20"); say Date.new("2019-01"); '
2019-01-20
Invalid Date string '2019-01'; use yyyy-mm-dd instead
  in block <unit> at -e line 1

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Edit Let's say I want to check if month is valid. In perl 5 it is so simple: 

use Time::Piece; localtime()->strptime(@ARGV[0], "%Y-%m");

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I don't care about date parsing, I don't look at string at all -- perl5 does that for me. 

bash$    perl -e 'use Time::Piece; localtime()->strptime(@ARGV[0], "%Y
+-%m"); print "ok\n"; '  "2019-01"
ok


bash$    perl -e 'use Time::Piece; localtime()->strptime(@ARGV[0], "%Y
+-%m"); print "ok\n"; '  "2019-77"
Error parsing time at /usr/lib/x86_64-linux-gnu/perl/5.26/Time/Piece.p
+m line 481.

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What is elegant way to do thatn in perl6?

Replies are listed 'Best First'.
Re: strptime("%Y-%m") in perl6
by choroba (Cardinal) on Feb 05, 2019 at 08:53 UTC
    Use the named parameters: 
    say Date.new(year => 2019, month => 1);

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    I don't see any other signature where the missing day would pass: 

    multi method new($year, $month, $day, :&formatter --> Date:D)
multi method new(:$year!, :$month = 1, :$day = 1  --> Date:D)
multi method new(Str $date                        --> Date:D)
multi method new(Instant:D $dt                    --> Date:D)
multi method new(DateTime:D $dt                   --> Date:D)

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    map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
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Re: strptime("%Y-%m") in perl6
by Laurent_R (Canon) on Feb 05, 2019 at 12:22 UTC
    choroba has provided a good solution. Depending on what you need exactly, this is another possible solution using a formatter (demonstrated here on the REPL): 
    > my $fmt = { sprintf "%04d-%02d", .year, .month };
-> ;; $_? is raw { #`(Block|173600432) ... }
> say Date.new(2019, 1, 1, formatter => $fmt);
2019-01

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    Update: Please note that you don't need to predefine the formatter: 
    > say Date.new(2019, 1, "1", formatter => { sprintf "%04d-%02d", .year
+, .month })
2019-01

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      Let's say I want to check if month is valid. In perl 5 it is so simple: 
      
use Time::Piece; localtime()->strptime(@ARGV[0], "%Y-%m");

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      I don't care about date parsing, I don't look at string at all -- perl5 does that for me. 
      
bash$    perl -e 'use Time::Piece; localtime()->strptime(@ARGV[0], "%Y
+-%m"); print "ok\n"; '  "2019-01"
ok


bash$    perl -e 'use Time::Piece; localtime()->strptime(@ARGV[0], "%Y
+-%m"); print "ok\n"; '  "2019-77"
Error parsing time at /usr/lib/x86_64-linux-gnu/perl/5.26/Time/Piece.p
+m line 481.

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      What is elegant way to do thatn in perl6?
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        But also 
        $ perl -MTime::Piece -le 'localtime()->strptime(shift, "%Y-%m-%d"); pr
+int "ok"'  2019-02-30
ok

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        map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
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        Nor sure to really understand your requirement, but what about this: 
        > for <1 5 3 13> -> $month { say Date.new(2019, $month, 1 )}
2019-01-01
2019-05-01
2019-03-01
Month out of range. Is: 13, should be in 1..12
  in block <unit> at <unknown file> line 1

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