(originally presented at YAPC::Europe::2007) No-one is as critical about something as those that love it dearly. Mark Fowler has been collecting complaints from professional Perl developers for years about what warts still remain with the language when strict and warnings are turned on. Are these problems unsolvable? A veteran Perl programmer himself Mark attempted to try and solve these issues - and then turned to the experts, the people who write books on Perl, the people who maintain the perl interpreter itself, for help. This is what he learned...

1. Perl Sucks!
(and what to do about it)

2. What this talk is not
• “Wah, no one uses ‘use strict’”
• “People’s perception of Perl is wrong”
• “The CPAN/mailing list/a other website
isn’t exactly how I like it”
• “The garbage collection de-allocation
routine isn’t very efficent”

3. What this talk is
• What’s a few major annoyances with Perl
• What we the humble programmer can do to
work around them

5. ~/bin

6. scp ~/bin nethost:

7. ssh newhost

8. jabme -m ‘compile done’

9. Module “Jabber::Lite”
not found

10. -bash: jabme: /usr/local/bin/
perl: bad interpreter: No
such file or directory

11. My Scripts Need
• A particular version of Perl
• A set of Perl modules

12. PAR

13. #!/usr/bin/perl
use strict;
use warnings;
use XML::LibXML;
use Template;
use DBD::SQLite;
use CGI;
use Parse::RecDescent;
use List::MoreUtils;
use Moose;
print quot;Hello Worldnquot;;

14. Make an executable
• perl -MCPAN -e ‘install PAR::Packer’
• pp -o hellow hellow.pl
• ...copy “hellow” to new computer
• ./hellow
Hello World

16. #!/usr/bin/perl
use strict;
use warnings;
print quot;Hello Worldnquot;;

18. Build our own Perl and
ship the whole thing

19. Get Stable Perl
• lwp-request $CPAN_URL >
perl-5.8.8.tar.gz
• gunzip -c perl-5.8.8.tar.gz | tar -xvf -
• cd perl-5.8.8

20. Tell it where to go
• mkdir -p /User/mark/bin/perl5.8.8
• ./configure.gnu --prefix=/User/mark/bin/
perl5.8.8

21. Install it
• make
• make test
• make install

22. We now have our own
perl in ~/bin

23. We can install it’s own
modules

24. ~/bin/perl5.8.8/bin/perl
-MCPAN -e ‘install
Template’

25. Problem: different paths
• /home/mark/bin/myperl
• /home/mfowler/bin/myperl
• /home/nisuser/bin/myperl

26. mv ~/bin/perl5.8.8
whatever

27. whatever/bin/perl -e
‘use Storable’

28. Can't locate Storable.pm in @INC (@INC
contains: /User/mark/bin/perl5.8.8/lib/5.8.8/
darwin-2level /User/mark/bin/perl5.8.8/lib/
5.8.8 /User/mark/bin/perl5.8.8/lib/site_perl/
5.8.8/darwin-2level /User/mark/bin/perl5.8.8/lib/
site_perl/5.8.8 /User/mark/bin/perl5.8.8/lib/
site_perl .) at -e line 1.

29. Can't locate Storable.pm in @INC (@INC
contains: /User/mark/bin/perl5.8.8/lib/5.8.8/
darwin-2level /User/mark/bin/perl5.8.8/lib/
5.8.8 /User/mark/bin/perl5.8.8/lib/site_perl/
5.8.8/darwin-2level /User/mark/bin/perl5.8.8/lib/
site_perl/5.8.8 /User/mark/bin/perl5.8.8/lib/
site_perl .) at -e line 1.

30. Can't locate Storable.pm in @INC (@INC
contains: ../lib/5.8.8/darwin-2level
../lib/5.8.8
../lib/site_perl/5.8.8/darwin-2level
../lib/site_perl/5.8.8
../lib/site_perl .) at -e line 1.

31. bleed to the rescue

32. B
E
TA
Get Bleed Perl
• lwp-request $CPAN_URL >
perl-5.9.5.tar.gz
• gunzip -c perl-5.9.5.tar.gz | tar -xvf -
• cd perl-5.9.5

33. B
E
TA
Tell it where to go
• mkdir -p /User/mark/bin/perl5.9.5
• ./Configure -Dusedevel -Dprefix=/User/
mark/bin/perl5.9.5 -Duserelocatableinc -d

34. B
E
TA
Tell it where to go
• mkdir -p /User/mark/bin/perl5.9.5
• ./Configure -Dusedevel -Dprefix=/User/
mark/bin/perl5.9.5 -Duserelocatableinc -d

35. B
E
TA
Install it
• make
• make test
• make install

36. B
E
TA
mv ~/bin/perl5.9.5
whatever

37. B
E
TA
whatever/bin/perl5.9.5
-e ‘use Storable’

38. Exception Handling

39. Java
try {
throw new NoCheeseException(“redo”);
} catch (NoCheeseException e) {
system.err.println(e.toString());
}

40. Perl
eval {
die new NoCheeseError->new(“redo”);
};
if (blessed($@) &&
$@->isa(“NoCheeseException”)) {
print STDERR $@;
} elsif ($@) { die $@ }

41. Perl has SUCKY
SYNTAX

42. Sins include:

43. Perl
eval {
die new NoCheeseError->new(“redo”);
};
if (blessed($@) &&
$@->isa(“NoCheeseException”)) {
print STDERR $@;
} elsif ($@) { die $@ }

44. die “stop my program”;

45. die “some catchable exception”;

46. Perl
eval {
die new NoCheeseError->new(“redo”);
};
if (blessed($@) &&
$@->isa(“NoCheeseException”)) {
print STDERR $@;
} elsif ($@) { die $@ }

47. eval “some code to be compiled”;

48. eval {
# run some code to catch errors in
};

49. Perl
eval {
die new NoCheeseError->new(“redo”);
};
if (blessed($@) &&
$@->isa(“NoCheeseException”)) {
print STDERR $@;
} elsif ($@) { die $@ }

50. Perl
eval {
die new NoCheeseError->new(“redo”);
};
if (blessed($@) &&
$@->isa(“NoCheeseException”)) {
print STDERR $@;
} elsif ($@) { die $@ }

51. We can fix it!

52. (still) Perl
try {
throw NoCheeseException “redo”;
}
catch NoCheeseException with {
print STDERR $@;
};

53. try {
throw NoCheeseException “redo”;
}
catch NoCheeseException with {
print STDERR $@;
}
catch AnotherError with {
print STDERR “oopsn”;
};

54. try {
throw NoCheeseException “redo”;
}
catch NoCheeseException with {
print STDERR $@;
}
catch AnotherError with {
print STDERR “oopsn”;
};

55. try( sub {
throw NoCheeseException “redo”;
},
catch NoCheeseException with(sub {
print STDERR $@;
},
catch AnotherError with(sub {
print STDERR “oopsn”;
})));

56. try( sub {
throw NoCheeseException “redo”;
},
catch NoCheeseException with(sub {
print STDERR $@;
},
catch AnotherError with(sub {
print STDERR “oopsn”;
})));

57. try( sub {
NoCheeseException->throw( “redo” );
},
NoCheeseException->catch( with(sub {
print STDERR $@;
},
AnotherError->catch( with(sub {
print STDERR “oopsn”;
})))));

58. sub with (&;@) {
return @_
}

59. try( sub {
NoCheeseException->throw( “redo” );
},
NoCheeseException->catch( with(sub {
print STDERR $@;
},
AnotherError->catch( with(sub {
print STDERR “oopsn”;
})))));

60. try( sub {
NoCheeseException->throw( “redo” );
},
NoCheeseException->catch( sub {
print STDERR $@;
},
AnotherError->catch( sub {
print STDERR “oopsn”;
})));

61. package OurErrorSuperclass;
sub catch {
my $class = shift;
my $action = shift;
return +{
class => $class,
action => $action
}, @_;
}

62. try( sub {
NoCheeseException->throw( “redo” );
},
NoCheeseException->catch( sub {
print STDERR $@;
},
AnotherError->catch( sub {
print STDERR “oopsn”;
})));

63. try( sub {
NoCheeseException->throw( “redo” );
},
NoCheeseException->catch( sub {
print STDERR $@;
}, +{
class => “AnotherError”,
action => sub { print STDERR “oopsn” }
}));

64. try( sub {
NoCheeseException->throw( “redo” );
}, +{
class => “NoCheeseException”,
action => sub { print STDERR $@; }
}, +{
class => “AnotherError”,
action => sub { print STDERR “oopsn” }
});

65. try( sub {
NoCheeseException->throw( “redo” );
}, +{
class => “NoCheeseException”,
action => sub { print STDERR $@; }
}, +{
class => “AnotherError”,
action => sub { print STDERR “oopsn” }
});

66. try( sub {
NoCheeseException->throw( “redo” );
}, +{
class => “NoCheeseException”,
action => sub { print STDERR $@; }
}, +{
class => “AnotherError”,
action => sub { print STDERR “oopsn” }
});

67. try( sub {
NoCheeseException->throw( “redo” );
}, +{
class => “NoCheeseException”,
action => sub { print STDERR $@; }
}, +{
class => “AnotherError”,
action => sub { print STDERR “oopsn” }
});

68. (still) Perl
try {
throw NoCheeseException “redo”;
}
catch NoCheeseException with {
print STDERR $@;
};

69. sub foo {
try {
return “This doesn’t return from foo”;
}
catch NoCheeseException with {
print STDERR $@;
};
}

70. sub foo {
eval {
return “This doesn’t return from foo”;
};
if ($@) { .... }
}

71. sub foo {
try {
return “This doesn’t return from foo”;
}
catch NoCheeseException with {
print STDERR $@;
};
}

72. sub foo {
try {
rreturn “This doesn’t return from foo”;
}
catch NoCheeseException with {
print STDERR $@;
} and return allowed;
}

73. sub foo {
try {
rreturn “This doesn’t return from foo”;
}
catch NoCheeseException with {
print STDERR $@;
} and return allowed;
}

74. MyException
NoDairyException
NoSpreadException
NoMilkException
NoButterException
NoMargException
NoCheeseException
NoEdamException NoStiltonException NoBrieException

75. package NoDairyException;
our @ISA = qw(MyError);
package NoMilkException;
our @ISA = qw(NoDairyException);
package NoSpreadException;
our @ISA = qw(NoDairyException);
package NoButterException;
our @ISA = qw(NoSpreadException);
package NoMargException;
our @ISA = qw(NoMargeException);
package NoCheeseException;
our @ISA = qw(NoDairyException);
package NoEdamException;
our @ISA = qw(NoCheeseException);
package NoStiltonException;
our @ISA = qw(NoCheeseException);
package NoBrieException;
our@ISA = qw(NoCheeseException);

76. Exceptions::define {
exception NoDairyException;
exception NoSpreadException extends NoDairyException;
exception NoButterException extends NoSpreadException;
exception NoMargException extends NoSpreadException;
exception NoMilkException extends NoDairyException;
exception NoCheeseException extends NoDairyException;
exception NoEdamException extends NoCheeseException;
exception NoStiltonException extends NoCheeseException;
exception NoBrieException extends NoCheeseException;
};

77. But it’s a scripting
language!

78. Don’t you just love the
Template Toolkit?

79. bash$ tpage
[% FOR a = [1..5]; a; END %]
^D
12345
bash$

80. #!perl
$whereami = “Vienna”;
print “Hello $whereami!n”;

81. #!tpage
[% whereami = “Vienna” -%]
Hello [% whereami %]!

82. bash$ ./hellov.tp

83. bash$ ./hellov.tp
-bash: ./hellov.tp: tpage: bad interpreter:
No such file or directory

84. where bash finds the
Executable code to
#!tpage load into memory
[% whereami = “Vienna” -%]
Hello [% whereami %]!

85. bash$ cat tpage
#!/usr/bin/perl -w
use strict;
use Template;
use AppConfig;
…

86. Two possible solutions

87. Method one:
Abuse source filters

88. • “Source filters are a way to change your
source code before perl gets to see it”

89. #!/usr/bin/perl
use strict;
use warnings;
use EnableDebugging;
# DEBUG printing stuff out
print quot;hinquot;;

90. #!/usr/bin/perl
use strict;
use warnings;
use EnableDebugging;
;print STDERR “DEBUG: printing stuff outn”;
print quot;hinquot;;

91. package EnableDebugging;
use Filter::Simple;
FILTER {
s{#s*DEBUGs+(.*)}
{;print STDERR q<DEBUG: $1>, quot;nquot;;};
};
1;

92. package EnableDebugging;
use Filter::Simple;
FILTER {
s{#s*DEBUGs+(.*)}
{;print STDERR q<DEBUG: $1>, quot;nquot;;};
};
1;

93. package tpage;
use Filter::Simple;
FILTER {
s{#s*DEBUGs+(.*)}
{;print STDERR q<DEBUG: $1>, quot;nquot;;};
};
1;

94. package tpage;
use Filter::Simple;
FILTER {
s{#s*DEBUGs+(.*)}
{;print STDERR q<DEBUG: $1>, quot;nquot;;};
};
1;

95. package tpage;
use Filter::Simple;
FILTER {
$template .= $_;
$_ = “”;
};
1;

96. package tpage;
use Filter::Simple;
FILTER {
$template .= $_;
$_ = “”;
};
END {
use Template;
Template->new->process($template);
}

97. #!/usr/bin/perl
use tpage;
[%- whereami = “Vienna” -%]
Hello [% whereami %]!

98. 2. Build our own
executable

99. #include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
int main(int argc, char **argv, char **env)
{
char *embedding[] = { quot;quot;, quot;-equot;, quot;0quot; };
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, 3, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
eval_pv(quot;print qq'oh hain’;quot;, TRUE);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}

100. ( stolen from
“perldoc perlembed”)

101. #include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
int main(int argc, char **argv, char **env)
{
char *embedding[] = { quot;quot;, quot;-equot;, quot;0quot; };
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, 3, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
eval_pv(quot;print qq'o hain';quot;, TRUE);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}

102. #include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
int main(int argc, char **argv, char **env)
{
char *embedding[] = { quot;quot;, quot;-equot;, quot;0quot; };
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, 3, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
eval_pv(quot;print qq’o hain’;quot;, TRUE);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}

103. cc -o hellow hellow.c `perl -MExtUtils::Embed -e ccopts -e ldopts`

104. bash$ ./hellow
o hai

105. #include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
int main(int argc, char **argv, char **env)
{
char *embedding[] = { quot;quot;, quot;-equot;, quot;0quot; };
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, 3, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
eval_pv(quot;print qq'o hain';quot;, TRUE);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}

106. #include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
int main(int argc, char **argv, char **env)
{
char *embedding[] = { quot;quot;, quot;-equot;, quot;0quot; };
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, 3, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
eval_pv(quot;print qq’o hain’;quot;, TRUE);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}

107. #include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
int main(int argc, char **argv, char **env)
{
char *embedding[] = { quot;quot;, quot;-equot;, quot;0quot;, argv[0]};
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, 4, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
eval_pv(quot;print qq’o hain’;quot;, TRUE);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}

108. #include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
int main(int argc, char **argv, char **env)
{
char *embedding[] = { quot;quot;, quot;-equot;, quot;0quot;, argv[0]};
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, 4, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
eval_pv(quot;print qq’o hain’;quot;, TRUE);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}

109. #include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
int main(int argc, char **argv, char **env)
{
char *embedding[] = { quot;quot;, quot;-equot;, quot;0quot;, argv[0]};
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, 4, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
eval_pv( “use Template
Template->new->process($ARGV[0])quot;, TRUE);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}

110. cc -o mytt mytt.c `perl -MExtUtils::Embed -e ccopts -e ldopts`

111. now Executable code to
load into memory
#!mytt
[% whereami = “Vienna” -%]
Hello [% whereami %]!

112. #include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
“hellov.tp”
int main(int argc, char **argv, char **env)
{
char *embedding[] = { quot;quot;, quot;-equot;, quot;0quot;, argv[0]};
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, 4, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
eval_pv( “use Template
Template->new->process($ARGV[0])quot;, TRUE);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}

113. #include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
“hellov.tp”
int main(int argc, char **argv, char **env)
{
char *embedding[] = { quot;quot;, quot;-equot;, quot;0quot;, argv[0]};
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, 4, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
perl_run(my_perl);
eval_pv( “use Template
Template->new->process($ARGV[0])quot;, TRUE);
perl_destruct(my_perl);
perl_free(my_perl);
PERL_SYS_TERM();
}

115. A
LP
H
A
We’ve already seen
source filters

116. B
E
TA
PPI
• Pure Perl parser
• Only parses a subset of Perl
• Can’t tell the difference between certain
Perl constructs
• This said - very very good at what it does

117. A
LP
H
A
MAD

118. A
LP
H
A
./configure.gnu --prefix=~/bin/perl595
-Dusedevel -Dmad=y
make && make test && make install

119. A
LP
H
A
my $a = 1;
my $b = 2;
print $a + $b;

120. A
LP
H
A
PERL_XMLDUMP=quot;foo.xmlquot; ./perl foo.pl

121. </op_nextstate>
A
LP
<op_sassign seq=quot;9 -> 10quot;
H
flags=quot;VOID,KIDS,STACKEDquot;> A
<op_leave seq=quot;0 -> DONEquot; targ=quot;1quot; flags=quot;VOID,KIDS,PARENSquot;
private=quot;REFCOUNTEDquot;
refcnt=quot;1quot;>
<op_enter seq=quot;1 -> 2quot; />
<op_null seq=quot;0 -> (2)quot; flags=quot;VOIDquot;>
<madprops>
<mad_sv key=quot;;quot; val=quot;quot;/>
</madprops>
<madprops>
</op_null>
<op_nextstate seq=quot;2 -> 3quot; flags=quot;VOIDquot;
line=quot;1quot;
package=quot;mainquot;>
<madprops>
<mad_sv key=quot;;quot; val=quot;;quot;/>
<mad_sv key=quot;#;quot; val=quot;&#xA;quot;/>
</madprops>
<mad_sv key=quot;oquot; val=quot;=quot;/>
</op_nextstate>
<op_sassign seq=quot;5 -> 6quot; flags=quot;VOID,KIDS,STACKEDquot;>
<madprops>
<mad_sv key=quot;oquot; val=quot;=quot;/>
<mad_sv key=quot;_oquot; val=quot; quot;/>
</madprops>
<op_const seq=quot;3 -> 4quot; flags=quot;SCALARquot;
IV=quot;1quot;>
<mad_sv key=quot;_oquot; val=quot; quot;/>
<madprops>
<mad_sv key=quot;Xquot; val=quot;1quot;/>
<mad_sv key=quot;_Xquot; val=quot; quot;/>
</madprops>
</op_const>
<op_padsv seq=quot;4 -> 5quot; targ=quot;1quot; flags=quot;SCALAR,REF,MOD,SPECIALquot;
private=quot;INTROquot;>
<madprops>
</madprops>
<mad_sv key=quot;$quot; val=quot;$aquot;/>
<mad_sv key=quot;_$quot; val=quot; quot;/>
<mad_sv key=quot;dquot; val=quot;myquot;/>
<mad_sv key=quot;_dquot; val=quot;quot;/>
</madprops>
</op_padsv>
</op_sassign>
<op_nextstate seq=quot;6 -> 7quot; flags=quot;VOIDquot;
<op_const seq=quot;7 -> 8quot; flags=quot;SCALARquot;
line=quot;2quot;
package=quot;mainquot;>
<madprops>
<mad_sv key=quot;;quot; val=quot;;quot;/>
<mad_sv key=quot;#;quot; val=quot;&#xA;quot;/>
</madprops>
</op_nextstate>
<op_sassign seq=quot;9 -> 10quot; flags=quot;VOID,KIDS,STACKEDquot;>
<madprops>
IV=quot;2quot;>
<mad_sv key=quot;oquot; val=quot;=quot;/>
<mad_sv key=quot;_oquot; val=quot; quot;/>
</madprops>
<op_const seq=quot;7 -> 8quot; flags=quot;SCALARquot;
IV=quot;2quot;>
<madprops>
<mad_sv key=quot;Xquot; val=quot;2quot;/>
<mad_sv key=quot;_Xquot; val=quot; quot;/>
<madprops>
</madprops>
</op_const>
<op_padsv seq=quot;8 -> 9quot; targ=quot;2quot; flags=quot;SCALAR,REF,MOD,SPECIALquot;
private=quot;INTROquot;>
<madprops>
<mad_sv key=quot;$quot; val=quot;$bquot;/>
<mad_sv key=quot;_$quot; val=quot; quot;/>
<mad_sv key=quot;dquot; val=quot;myquot;/>
<mad_sv key=quot;Xquot; val=quot;2quot;/>
</madprops>
</op_padsv>
</op_sassign>
<op_nextstate seq=quot;10 -> 11quot; flags=quot;VOIDquot;
line=quot;3quot;
package=quot;mainquot;>
<madprops>
<mad_sv key=quot;;quot; val=quot;;quot;/>
<mad_sv key=quot;_Xquot; val=quot; quot;/>
<mad_sv key=quot;_;quot; val=quot;quot;/>
<mad_sv key=quot;#;quot; val=quot;&#xA;quot;/>
</madprops>
</op_nextstate>
<op_print seq=quot;15 -> 16quot; flags=quot;SCALAR,KIDSquot;>
<madprops>
<mad_sv key=quot;oquot; val=quot;printquot;/>
</madprops>
</madprops>
<op_pushmark seq=quot;11 -> 12quot; flags=quot;SCALARquot; />
<op_add seq=quot;14 -> 15quot; targ=quot;3quot; flags=quot;SCALAR,KIDSquot;>
<madprops>
<mad_sv key=quot;oquot; val=quot;+quot;/>
<mad_sv key=quot;_oquot; val=quot; quot;/>
</madprops>
<op_padsv seq=quot;12 -> 13quot; targ=quot;1quot; flags=quot;SCALARquot;>
<madprops>
</op_const>
<mad_sv key=quot;$quot; val=quot;$aquot;/>
<mad_sv key=quot;_$quot; val=quot; quot;/>
</madprops>
</op_padsv>
<op_padsv seq=quot;13 -> 14quot; targ=quot;2quot; flags=quot;SCALARquot;>
<madprops>
<mad_sv key=quot;$quot; val=quot;$bquot;/>
<mad_sv key=quot;_$quot; val=quot; quot;/>
</madprops>
<op_padsv seq=quot;8 -> 9quot; targ=quot;2quot;
</op_padsv>
</op_add>
</op_print>
<op_null seq=quot;0 -> (16)quot; flags=quot;VOIDquot; />
</op_leave>
flags=quot;SCALAR,REF,MOD,SPECIALquot;

122. B::Generate
• Can be used to create OP codes (i.e.
compiled Perl code) directly from Perl

123. use B::Generate;
# Do nothing, slowly.
CHECK {
my $null = new B::OP(quot;nullquot;,0);
my $enter = new B::OP(quot;enterquot;,0);
my $cop = new B::COP(0, quot;hiyaquot;, 0);
my $leave = new B::LISTOP(quot;leavequot;, 0, $enter, $null);
$leave->children(3);
$enter->sibling($cop);
$enter->next($cop);
$cop->sibling($null);
$null->next($leave);
$cop->next($leave);
# Tell Perl where to find our tree.
B::main_root($leave);
B::main_start($enter);
}

124. optomize.pm
• Can be used to manipulate the OP codes
after they’ve loaded
• Kinda like source filters for compiled
bypecode

125. Use?
• PPI is reliable, but limited in it’s ability
• Easy to try to do too much with
• Other techniques are very unstable / new
• B::Generate
• optomize
• MAD

127. A
LP
H
A
package main;
use typesafety; # 'summary', 'debug';
my FooBar $foo; # establish type-checked variables
my FooBar $bar; # FooBar is the base class of references $bar will hold
my BazQux $baz;
$foo = new FooBar; # this is okay, because $foo holds FooBars
$bar = $foo; # this is okay, because $bar also holds FooBars
# $foo = 10; # this would throw an error - 10 is not a FooBar
# $baz = $foo; # not allowed - FooBar isn't a BazQux
$foo = $baz; # is allowed - BazQux is a FooBar because of inheritance
$bar = $foo->foo($baz, 1); # this is okay, as FooBar::foo() returns FooBars also
typesafety::check(); # perform type check static analysis

128. A
LP
H
A
package main;
use typesafety; # 'summary', 'debug';
my FooBar $foo; # establish type-checked variables
my FooBar $bar; # FooBar is the base class of references $bar will hold
my BazQux $baz;
$foo = new FooBar; # this is okay, because $foo holds FooBars
$bar = $foo; # this is okay, because $bar also holds FooBars
# $foo = 10; # this would throw an error - 10 is not a FooBar
# $baz = $foo; # not allowed - FooBar isn't a BazQux
$foo = $baz; # is allowed - BazQux is a FooBar because of inheritance
$bar = $foo->foo($baz, 1); # this is okay, as FooBar::foo() returns FooBars also
typesafety::check(); # perform type check static analysis

129. A
LP
H
A
package main;
use typesafety; # 'summary', 'debug';
my FooBar $foo; # establish type-checked variables
my FooBar $bar; # FooBar is the base class of references $bar will hold
my BazQux $baz;
$foo = new FooBar; # this is okay, because $foo holds FooBars
$bar = $foo; # this is okay, because $bar also holds FooBars
# $foo = 10; # this would throw an error - 10 is not a FooBar
# $baz = $foo; # not allowed - FooBar isn't a BazQux
$foo = $baz; # is allowed - BazQux is a FooBar because of inheritance
$bar = $foo->foo($baz, 1); # this is okay, as FooBar::foo() returns FooBars also
typesafety::check(); # perform type check static analysis

130. A
LP
H
A
package main;
use typesafety; # 'summary', 'debug';
my FooBar $foo; # establish type-checked variables
my FooBar $bar; # FooBar is the base class of references $bar will hold
my BazQux $baz;
$foo = new FooBar; # this is okay, because $foo holds FooBars
$bar = $foo; # this is okay, because $bar also holds FooBars
# $foo = 10; # this would throw an error - 10 is not a FooBar
# $baz = $foo; # not allowed - FooBar isn't a BazQux
$foo = $baz; # is allowed - BazQux is a FooBar because of inheritance
$bar = $foo->foo($baz, 1); # this is okay, as FooBar::foo() returns FooBars also
typesafety::check(); # perform type check static analysis