From jacoby.david at gmail.com  Wed Dec 18 10:53:07 2019
From: jacoby.david at gmail.com (Dave Jacoby)
Date: Wed, 18 Dec 2019 13:53:07 -0500
Subject: [Purdue-pm] TIL
Message-ID: <CAGbe8xoKSu3h8G72kUtZvxNtsL823a+PQAFccxxMuHHUyTjGgw@mail.gmail.com>

use JSON;
use PerlX::Maybe qw{ maybe provided };

my $json = JSON->new->canonical;

for my $i ( 1 .. 5 ) {
    my $x;
    $x = 1 if int rand 2;
    my $data = { maybe x1 => $x, x2 => $x, provided $i > 3, i => $i, };
    say $json->encode($data);
}

$ ./maybe.pl
{"x1":1,"x2":1}
{"x1":1,"x2":1}
{"x2":null}
{"i":4,"x1":1,"x2":1}
{"i":5,"x2":null}

x1 will always be a thing, but the value will be undefined half the time.

x2 will not be assigned unless the value it it defined exists. we get this
from `maybe`.

This is roughly

if ( defined $x ) { $data->{x2} = $x }

but so much more concise.

`provided` gives us conditionals.

if ( $i > 3 ) { $data->{$i} = $i }

becomes

provided $i > $3 , i => $i

it's small, among the smallest things thrown at me recently, but if nothing
else, it makes a smaller JSON string when used.

-- 
Dave Jacoby
jacoby.david at gmail.com

I deal with my software the way I treat my eldritch abomination:
 It's not human, it's not even alive in the natural sense.
 It's nightmare-born and nightmare-shaped, and nightmares don't die easy.
  -- @yenzie
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From mark at purdue.edu  Thu Dec 19 23:09:27 2019
From: mark at purdue.edu (Mark Senn)
Date: Fri, 20 Dec 2019 02:09:27 -0500
Subject: [Purdue-pm] TIL
In-Reply-To: <CAGbe8xoKSu3h8G72kUtZvxNtsL823a+PQAFccxxMuHHUyTjGgw@mail.gmail.com>
References: <CAGbe8xoKSu3h8G72kUtZvxNtsL823a+PQAFccxxMuHHUyTjGgw@mail.gmail.com>
Message-ID: <23145.1576825767@pier.ecn.purdue.edu>

Dave Jacoby <jacoby.david at gmail.com> wrote on 2019-12-18 at 18:53+00:
> use JSON;
> use PerlX::Maybe qw{ maybe provided };
> 
> my $json = JSON->new->canonical;
> 
> for my $i ( 1 .. 5 ) {
>     my $x;
>     $x = 1 if int rand 2;
>     my $data = { maybe x1 => $x, x2 => $x, provided $i > 3, i => $i, };
>     say $json->encode($data);
> }
> 
> $ ./maybe.pl
> {"x1":1,"x2":1}
>  {"x1":1,"x2":1}
> {"x2":null}
> {"i":4,"x1":1,"x2":1}
> {"i":5,"x2":null}
> 
> x1 will always be a thing, but the value will be undefined half the time.
> 
> x2 will not be assigned unless the value it it defined exists. we get this
> from `maybe`.
> 
> This is roughly
> 
> if ( defined $x ) { $data->{x2} = $x }
> 
> but so much more concise.
> 
> `provided` gives us conditionals.
> 
> if ( $i > 3 ) { $data->{$i} = $i }
> 
> becomes
> 
> provided $i > $3 , i => $i
> 
> it's small, among the smallest things thrown at me recently, but if nothing
> else, it makes a smaller JSON string when used.



Here is how I would do this in Raku.    -mark

#
# From "The JSON Data Interchange Syntax", second edition, December 2017,
# retrieved from
#     http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf
# on 2019-12-20 at 06:31+00:
#     A JSON value can be an object, array,
#     number, string, true, false, or null.
# There is no "undefined" in JSON so it is my understanding is that a
# name that is not set (i.e., is not in a JSON file) is the same as
# setting that name to "null".
#
# I'd do the above using the following code in Raku (formerly known
# as Perl 6).
#

# Use version 6.d of the Raku language specification.
# This will cause Perl 5 to complain if you try to use
# Perl 5 to run this program.
use v6.d;

use JSON::Class;

class Triple does JSON::Class
{
    has Int $.i  is rw;
    has Int $.x1 is rw;
    has Int $.x2 is rw;
}

for 1..5 -> $i
{
    $_ = Triple.new();

    ($i > 3)  and  $_.i = $i;

    (Bool.pick)  and  $_.x1 = $_.x2 = 1;

    # This program doesn't set names to "null" but if it
    # did the ":skip-null" below would not print them out.
    say $_.to-json():skip-null;
}