The document discusses various techniques for dumping and pretty printing Perl 6 objects and data structures. It shows examples of using regular expressions to match strings, and then dumping the match object. It also demonstrates different modules and approaches for customizing how objects are formatted and printed, including adding type-specific handling and decorating the dumper object. The goal is to produce human-readable output rather than eval-able code like Data::Dumper.

1. Dumping
Perl 6
AmsterdamX.pm, 8 Jun 2017

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DumpingPerl6
Sponsored in part by a grant from

3. ThePerlReview•www.theperlreview.com
DumpingPerl6
Plain
my $rx = rx/ <[ a .. z ]> <[ 1 .. 9 ]> /;
my $string = ':::abc123::';
my $match = $string ~~ $rx;
put $match;
c1

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DumpingPerl6
.gist
my $rx = rx/ <[ a .. z ]> <[ 1 .. 9 ]> /;
my $string = ':::abc123::';
my $match = $string ~~ $rx;
say $match; # put $match.gist
｢c1｣

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DumpingPerl6
.perl
my $rx = rx/ <[ a .. z ]> <[ 1 .. 9 ]> /;
my $string = ':::abc123::';
my $match = $string ~~ $rx;
put $match.perl;
Match.new(list => (), made => Any,
pos => 7, hash => Map.new(()), orig =>
":::abc123::", from => 5)

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DumpingPerl6
Pretty::Printer
use Pretty::Printer; # From Jeff Goff
my $rx = rx/ <[ a .. z ]> <[ 1 .. 9 ]> /;
my $string = ':::abc123::';
my $match = $string ~~ $rx;
Pretty::Printer.new.pp: $match;
Any

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DumpingPerl6
method _pp($ds,$depth)
{
my Str $str;
given $ds.WHAT
{
when Hash { $str ~= self.Hash($ds,$depth) }
when Array { $str ~= self.Array($ds,$depth) }
when Pair { $str ~= self.Pair($ds,$depth) }
when Str { $str ~= $ds.perl }
when Numeric { $str ~= ~$ds }
when Nil { $str ~= q{Nil} }
when Any { $str ~= q{Any} }
}
return self.indent-string($str,$depth);
}

8. ThePerlReview•www.theperlreview.com
DumpingPerl6
PrettyDump
use PrettyDump;
my $rx = rx/ <[ a .. z ]> <[ 1 .. 9 ]> /;
my $string = ':::abc123::';
my $match = $string ~~ $rx;
put PrettyDump.new.dump: $match;

9. ThePerlReview•www.theperlreview.com
DumpingPerl6
Match.new(
:from(5),
:hash(Map.new()),
:list($()),
:made(Mu),
:orig(":::abc123::"),
:pos(7),
:to(7)
)

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DumpingPerl6
By Type

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DumpingPerl6
method _pp($ds,$depth)
{
my Str $str;
given $ds.WHAT
{
# Check more derived types first.
when Match { $str ~= self.Match($ds,$depth) }
when Hash { $str ~= self.Hash($ds,$depth) }
when Array { $str ~= self.Array($ds,$depth) }
when Map { $str ~= self.Map($ds,$depth) }
when List { $str ~= self.List($ds,$depth) }
when Pair { $str ~= self.Pair($ds,$depth) }
when Str { $str ~= $ds.perl }
when Numeric { $str ~= ~$ds }
when Nil { $str ~= q{Nil} }
when Any { $str ~= q{Any} }
}
return self.indent-string($str,$depth);
}

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DumpingPerl6
Per Class

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DumpingPerl6
class SomeClass {
…
method PrettyDump ( $pretty, $ds, $depth ) {
…
}
}
my $pretty = PrettyDump.new;
my $some-object = SomeClass.new;
put $pretty.dump: $some-object;

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DumpingPerl6
use PrettyDump;
my $pretty = PrettyDump.new;
my Int $a = 137;
put $pretty.dump: $a;
my $b = $a but role {
method PrettyDump ( $pretty, $depth = 0 ) {
"({self.^name}) {self}";
}
};
put $pretty.dump: $b;

15. ThePerlReview•www.theperlreview.com
DumpingPerl6
method dump ( $ds, $depth = 0 ) {
put "In dump. Got ", $ds.^name;
my Str $str;
if $ds.can: 'PrettyDump' {
$str ~= $ds.PrettyDump: self;
}
elsif $ds ~~ Numeric {
$str ~= self.Numeric: $ds, $depth;
}
elsif self.can: $ds.^name {
my $what = $ds.^name;
$str ~= self."$what"( $ds, $depth );
}
else {
die "Could not handle " ~ $ds.perl;
}
return self.indent-string: $str, $depth;
}

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DumpingPerl6
Per Object

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DumpingPerl6
Decorate the Dumper
my $pretty = PrettyDump.new;
class SomeClass { … }
my $handler = sub ( $pretty, $ds, Int $depth = 0 ) {
...
}
$pretty.add-handler: 'SomeClass', $handler;
put $pretty.dump: $SomeClass-object;

18. ThePerlReview•www.theperlreview.com
DumpingPerl6
method dump ( $ds, Int $depth = 0 --> Str ) {
my Str $str = do {
# If the PrettyDump object has a user-defined handler
# for this type, prefer that one
if self.handles: $ds.^name {
self!handle: $ds, $depth;
}
# The object might have its own method to dump
# its structure
elsif $ds.can: 'PrettyDump' {
$ds.PrettyDump: self;
}
# If it's any sort of Numeric, we'll handle it
# and dispatch further
elsif $ds ~~ Numeric {
self!Numeric: $ds, $depth;
}
…

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DumpingPerl6
# If we have a method name that matches the class, we'll
# use that.
elsif self.can: $ds.^name {
my $what = $ds.^name;
self."$what"( $ds, $depth );
}
# If the class inherits from something that we know
# about, use the most specific one that we know about
elsif $ds.^parents.grep(
{ self.can: $_.^name } ).elems > 0 {
my Str $str = '';
for $ds.^parents -> $type {
my $what = $type.^name;
next unless self.can( $what );
$str ~= self."$what"(
$ds, $depth, "{$ds.^name}.new(", ')' );
last;
}
$str;
}
…

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DumpingPerl6
# If we're this far and the object has a .Str method,
# we'll use that:
elsif $ds.can: 'Str' {
"({$ds.^name}): " ~ $ds.Str;
}
# Finally, we'll put a placeholder method there
else {
"(Unhandled {$ds.^name})"
}
};
return self!indent-string: $str, $depth;
}

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DumpingPerl6
Not Data::Dumper
• Does not produce eval-able code
• Does not know what it has already seen
• Missing a few formatting features

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DumpingPerl6
What else might it do?
• Handle more data types
• More configurable formatting options
• Formatting hooks
• Send email

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DumpingPerl6
Questions