NAME

Parse::Eyapp::Base - Miscellaneous support functions for Parse::Eyapp

SYNOPSIS

use Parse::Eyapp::Base qw(:all)

INTRODUCTION

Parse::Eyapp::Base holds a set of utility functions that give support to the other modules that made Parse::Eyapp. Several of them are related to the dynamic use of methods and subroutines.

SUBROUTINES

Function `insert_method`

Function insert_method receives as arguments a list of class names, the name of the method that will be inserted in such classes and a reference to the code implementing such method.

insert_method( qw{CLASS1 CLASS2 ... }, 'subname', sub { ... } )

It inserts the method in the specified classes. A second way to call it is without the last argument, the handler:

insert_method( qw{CLASS1 CLASS2 ... }, 'subname' )

In such case the function is deleted from all the specified classes and it no longer exists.

The caller class is assumed if no classes are specified:

insert_method('subname', sub { ... } )

See the following session with the debugger:

pl@nereida:~/src/perl/YappWithDefaultAction/lib/Parse/Eyapp$ perl -wde 0
main::(-e:1):   0
  DB<1> use Parse::Eyapp::Base qw(:all)
  DB<2> insert_method( qw{PLUS MINUS TIMES }, 'printclass', sub { print "$_[0]\n" } )
  DB<3> $_->printclass for qw{PLUS MINUS TIMES }
PLUS
MINUS
TIMES

  DB<4> insert_method( qw{PLUS MINUS TIMES }, 'printclass')
  DB<5> print $_->can('printclass')?"Yes\n":"No\n"  for qw{PLUS MINUS TIMES }
No
No
No

Function `insert_function`

It works as insert_method (see section "Function insert_method"), only that instead of classes receives the full names of the functions to install and a reference to the code implementing such function. See an example of call:

insert_function(
  qw{ FUNCTIONCALL::type_info VARARRAY::type_info VAR::type_info },
  \&type_info
);

When the package is unspecified the caller package is assumed. See the following example:

pl@nereida:~/src/perl/YappWithDefaultAction/lib/Parse/Eyapp$ perl -wde 0
main::(-e:1):   0
  DB<1> use Parse::Eyapp::Base qw(:all)
  DB<2> insert_function('Tutu::tata', 'titi', sub{ print "Inside titi\n"})
  DB<3> titi()
Inside titi

  DB<4> Tutu::tata()
Inside titi

Function `empty_method`

The call to

empty_method(qw{CLASSES ... }, 'subname')

is equivalent to

insert_method(qw{CLASSES ... }, 'subname', sub {})

Consequently empty_method replaces the current CODE for function subname by an empty subroutine

Function `push_method`

The call

push_method( qw{CLASS1 CLASS2 ... }, 'subname', sub { ... } )

saves the current methods CLASS1::subname, CLASS2::subname, etc. in a stack and proceeds to install the new handler specified through the last argument. See an example:

pl@nereida:~/src/perl/YappWithDefaultAction/lib/Parse/Eyapp$ perl -wde 0
main::(-e:1):   0
  DB<1> use Parse::Eyapp::Base qw(:all)
  DB<2> sub Tutu::titi { print "Inside first Tutu::titi!\n" }
  DB<3> push_method('Tutu', 'titi', sub { print "New titi!\n" })
  DB<4> Tutu::titi()
New titi!

  DB<5> pop_method('Tutu', 'titi')
  DB<6> Tutu::titi()
Inside first Tutu::titi!

  DB<7> push_method('Tutu', 'titi') # No handler: sub Tutu::titi no longer exists
  DB<8> print "Can't titi\n" unless Tutu->can('titi')
Can't titi

  DB<9> pop_method('Tutu', 'titi') # Give me the old sub
  DB<10> Tutu::titi()
Inside first Tutu::titi!

The caller class is assumed if no classes are specified.

In list context the push_method function returns an array of pointers to the old versions of the function. In a scalar context returns the first CODE reference. See the following example:

pl@nereida:~/src/perl/YappWithDefaultAction/examples$ cat -n returnedbypushmethod.pl
   1  #!/usr/local/bin/perl -w
   2  use strict;
   3  use Parse::Eyapp::Base qw(:all);
   4
   5  sub tutu { "tutu" }
   6  sub Chum::tutu { "chum" }
   7
   8  my @classes = qw{main Cham Chum};
   9
  10  my %oldf;
  11  our $tutu = 5;
  12  our @tutu = 9..12;
  13  $Cham::tutu = 8;
  14  @Cham::tutu = 1..3;
  15
  16  @oldf{@classes} = push_method(@classes, 'tutu', sub { "titi" });
  17
  18  print "Calling new function 'tutu':".&tutu()."\n";
  19
  20  for (@classes) {
  21    if (defined($oldf{$_})) {
  22      print "Old function 'tutu' in $_ gives: ".$oldf{$_}->()."\n";
  23    }
  24    else {
  25       print "Function 'tutu' wasn't defined in $_\n";
  26    }
  27  }

The following session with the debugger shows that:

Package variables with the same name like $tutu or @tutu aren't changed by insert_method
References to the old versions of function tutu are returned by insert_method

pl@nereida:~/LEyapp/examples$ perl -wd returnedbypushmethod.pl
main::(returnedbypushmethod.pl:8):
8:      my @classes = qw{main Cham Chum};
  DB<1> c 18
main::(returnedbypushmethod.pl:18):
18:     print "Calling new function 'tutu':".&tutu()."\n";
  DB<2> n
Calling new function 'tutu':titi
main::(returnedbypushmethod.pl:20):
20:     for (@classes) {
  DB<2> x @tutu
0  9
1  10
2  11
3  12
  DB<3> x @Cham::tutu
0  1
1  2
2  3
  DB<4> p $Cham::tutu
8
  DB<5> c
Old function 'tutu' in main gives: tutu
Function 'tutu' wasn't defined in Cham
Old function 'tutu' in Chum gives: chum

Function `pop_method`

The call

pop_method(qw{CLASS1 CLASS2 ... }, 'subname' )

pops the methods in the tops of the stacks associated with CLASS1::subname, CLASS2::subname, etc. See the example in the section push_method above.

The caller class is assumed if no classes are specified.

If the stack for CLASS::subname is empty the old specification of subname will remain.

pl@nereida:~/LEyapp/examples$ cat returnedbypopmethod.pl
#!/usr/local/bin/perl -w
use strict;
use Parse::Eyapp::Base qw(:all);

sub tutu { "tutu" }

my $old = pop_method('tutu');

print "Function 'tutu' is available\n" if main->can('tutu');
print "Old function 'tutu' gives: ".$old->()."\n";

When executed gives the following output:

pl@nereida:~/LEyapp/examples$ returnedbypopmethod.pl
Function 'tutu' is available
Old function 'tutu' gives: tutu

In list context the pop_method function returns an array of pointers to the old versions of the function. In a scalar context returns the first function reference. When the stack is empty the function(s) are deleted.

Examples of `push_method` and `pop_method`

Hiding functions

See the following example:

package Tutu;
use Parse::Eyapp::Base qw(:all);

sub tutu {
  print "Inside tutu\n"
}

sub plim {

  # When the stack is empty the old 'tutu' remains ...
  pop_method('tutu');

  &tutu(); # Inside tutu

  push_method('tutu'); # Tutu disapears
}

package main;

Tutu::plim(); 
# main can't call 'tutu'
print "Can't tutu\n" unless Tutu->can('tutu');
Tutu::plim();

When executed the former program produces this output:

pl@nereida:~/LEyapp/examples$ localsubbase.pl
Inside tutu
Can't tutu
Inside tutu

Changing the Behavior of Method-parametric Methods

A common situation where I need the couple (push_method, pop_method) is to control the behavior of method str when debugging:

pl@nereida:~/Lbook/code/Simple-Types/script$ perl -wd usetypes.pl prueba26.c 2
Loading DB routines from perl5db.pl version 1.28
Editor support available.
main::(usetypes.pl:5):  my $filename = shift || die "Usage:\n$0 file.c\n";
  DB<1> c Parse::Eyapp::Node::str
1 int f() {
2   int a[30];
3
4   return;
5 }
Parse::Eyapp::Node::str(/home/pl/src/perl/YappWithDefaultAction/lib//Parse/Eyapp/Node.pm:716):
716:      my @terms;

Let us assume I want to see the syntax tree for this program. I can see it using $_[0]->str but the problem is that nodes PROGRAM and FUNCTION have defined a footnote method that will dump their symbol and type tables producing hundred of lines of output and making difficult to see the shape of the tree. This is because method str calls method footnote wherever the node being visited can do footnote. The solution is to use push_method to make the footnote methods disappear:

DB<2> use Parse::Eyapp::Base qw(:all)
DB<3> push_method(qw{PROGRAM FUNCTION}, 'footnote')

The use of push_method without an explicit code handler eliminates the CODE entry for footnote:

  DB<4> p $_->can('footnote')? "1\n" : "0\n" for (qw{PROGRAM FUNCTION})
0
0

Now I can see the shape of the tree:

  DB<5> p $_[0]->str

PROGRAM(
  FUNCTION[f](
    EMPTYRETURN
  )
) # PROGRAM

If I want back the footnote methods I can use pop_method:

DB<6> pop_method(qw{PROGRAM FUNCTION}, 'footnote')
DB<7> p $_->can('footnote')? "1\n" : "0\n" for (qw{PROGRAM FUNCTION})
1
1

Now the information will be profuse:

  DB<8> p $_[0]->str

PROGRAM^{0}(
  FUNCTION[f]^{1}(
    EMPTYRETURN
  )
) # PROGRAM
---------------------------
0)
Types:
$VAR1 = {
  'CHAR' => bless( {
    'children' => []
  }, 'CHAR' ),
  ..... etc, etc.
  'A_30(INT)' => bless( {
    'children' => [
      $VAR1->{'INT'}
    ]
  }, 'A_30' )
};
Symbol Table:
$VAR1 = {
  'f' => {
    'type' => 'F(X_0(),INT)',
    'line' => 1
  }
};

---------------------------
1)
$VAR1 = {
  'a' => {
    'type' => 'A_30(INT)',
    'line' => 2
  }
};

You can still do something like this to achieve a similar effect:

DB<9> p eval { local (*PROGRAM::footnote, *FUNCTION::footnote) = (sub {}, sub {}); $_[0]->str }

PROGRAM(
  FUNCTION[f](
    EMPTYRETURN
  )
) # PROGRAM

but is certainly more verbose and does not eliminate function footnote from the PROGRAM and FUNCTION classes.

Therefore the usefulness of push_method is when you either want to temporarily delete your function/methods or localize them not necessarily in a scope basis.

Function `compute_lines`

The call

compute_lines(\$text, $filename, $pattern)

Substitutes all the occurrences of $pattern by #line $number $filename in string $text. where $number is the line number.

Function `slurp_file`

The call

my $input = slurp_file($filename, "c");

returns a string with the contents of the file $filename assuming extension "c".

 pl@nereida:~/src/perl/YappWithDefaultAction/lib/Parse/Eyapp$ perl -wde 0
 main::(-e:1):   0
   DB<1> use Parse::Eyapp::Base qw(:all)
   DB<2> !!ls *yp # There are two files with extension .yp in this directory
 Parse.yp  Treeregexp.yp
   DB<3> $x = slurp_file('Parse', 'yp') # read the whole file
   DB<4> p $x =~ tr/\n// # file Parse.yp has 1038 lines
 1038

Function `valid_keys`

The call

             valid_keys(%hash)

Returns a string with the keys of the %hash separated by commas:

pl@nereida:~/src/perl/YappWithDefaultAction/lib/Parse/Eyapp$ perl -wde 0
main::(-e:1):   0
  DB<1> use Parse::Eyapp::Base qw(:all)
  DB<2> %h = ( SCOPE_NAME => 'STRING', ENTRY_NAME => 'STRING', SCOPE_DEPTH => 'STRING')
  DB<3> $x = valid_keys(%h)
  DB<4> p $x
ENTRY_NAME, SCOPE_DEPTH, SCOPE_NAME

Function `invalid_keys`

It is called with two hash references:

  DB<5> p invalid_keys(\%h, { SCOPE_NAME => 'a', ENTRY_NAMe => 'b', SCOPE_DEPTH => 'c'})
ENTRY_NAMe

It returns the first key in the second hash that does not appear in the first hash. See a more complete example:

pl@nereida:~/src/perl/YappWithDefaultAction/lib/Parse/Eyapp$ head -31 Scope.pm | cat -n
   1  package Parse::Eyapp::Scope;
   2  use strict;
   3  use warnings;
   4  use Carp;
   5  use List::MoreUtils qw(part);
   6  use Parse::Eyapp::Base qw(valid_keys invalid_keys);
   7
   8  my %_new_scope = (
   9    SCOPE_NAME      => 'STRING',
  10    ENTRY_NAME      => 'STRING',
  11    SCOPE_DEPTH     => 'STRING',
  12  );
  13  my $valid_scope_keys = valid_keys(%_new_scope);
  14
  15  sub new {
  16   my $class = shift;
  17    my %args = @_;
  18
  19    if (defined($a = invalid_keys(\%_new_scope, \%args))) {
  20      croak("Parse::Eyapp::Scope::new Error!:\n"
  21           ."unknown argument $a. Valid arguments for new are:\n  $valid_scope_keys")
  22    }
  23    $args{ENTRY_NAME}      = 'entry' unless defined($args{ENTRY_NAME});
  24    $args{SCOPE_NAME}      = 'scope' unless defined($args{SCOPE_NAME});
  25    $args{SCOPE_DEPTH}     = ''      unless defined($args{SCOPE_DEPTH});
  26    $args{PENDING_DECL}    = [];
  27    $args{SCOPE_MARK}      = 0;
  28    $args{DEPTH}           = -1; # first depth is 0
  29
  30    bless \%args, $class;
  31  }

Function `write_file`

The call

write_file($filename, $textref)

simply opens a file with name $filename writes in it the text referenced by $texterf and closes the file

Function `numbered`

The call

numbered($input)

Returns a string like $input but with lines numbered and the numbers correctly indented. See an example:

  DB<1> use Parse::Eyapp::Base qw(:all)
  DB<2> $input = "Another line!\n"x12
  DB<3> $output = numbered($input)
  DB<4> p $output
 1 Another line!
 2 Another line!
 3 Another line!
 4 Another line!
 5 Another line!
 6 Another line!
 7 Another line!
 8 Another line!
 9 Another line!
10 Another line!
11 Another line!
12 Another line!

CONTRIBUTORS

Hal Finkel http://www.halssoftware.com/
G. Williams http://kasei.us/
Thomas L. Shinnick http://search.cpan.org/~tshinnic/
Frank Leray

AUTHOR

Casiano Rodriguez-Leon (casiano@ull.es)

ACKNOWLEDGMENTS

This work has been supported by CEE (FEDER) and the Spanish Ministry of Educacion y Ciencia through Plan Nacional I+D+I number TIN2005-08818-C04-04 (ULL::OPLINK project http://www.oplink.ull.es/). Support from Gobierno de Canarias was through GC02210601 (Grupos Consolidados). The University of La Laguna has also supported my work in many ways and for many years.

A large percentage of code is verbatim taken from Parse::Yapp 1.05. The author of Parse::Yapp is Francois Desarmenien.

I wish to thank Francois Desarmenien for his Parse::Yapp module, to my students at La Laguna and to the Perl Community. Thanks to the people who have contributed to improve the module (see "CONTRIBUTORS" in Parse::Eyapp). Thanks to Larry Wall for giving us Perl. Special thanks to Juana.

LICENCE AND COPYRIGHT

These modules are free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

To install Parse::Eyapp, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Parse::Eyapp

CPAN shell

perl -MCPAN -e shell
install Parse::Eyapp

For more information on module installation, please visit the detailed CPAN module installation guide.

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NAME

SYNOPSIS

INTRODUCTION

SUBROUTINES

Function insert_method

Function insert_function

Function empty_method

Function push_method

Function pop_method

Examples of push_method and pop_method

Hiding functions

Changing the Behavior of Method-parametric Methods

Function compute_lines

Function slurp_file

Function valid_keys

Function invalid_keys

Function write_file

Function numbered

SEE ALSO

CONTRIBUTORS

AUTHOR

ACKNOWLEDGMENTS

LICENCE AND COPYRIGHT

Module Install Instructions

Function `insert_method`

Function `insert_function`

Function `empty_method`

Function `push_method`

Function `pop_method`

Examples of `push_method` and `pop_method`

Function `compute_lines`

Function `slurp_file`

Function `valid_keys`

Function `invalid_keys`

Function `write_file`

Function `numbered`