/ 
Devel-REPL-1.003018
River stage two • 23 direct dependents • 34 total dependents
/ Devel::REPL::Overview

NAME

Devel::REPL::Overview - overview of Devel::REPL.

DESCRIPTION

What is a console? How it can assist you?

Most modern languages have consoles. Console is an interactive tool
that evaluates your input while you type it.
It gives you several advantages:

  • Quickly test some thought or tricky expression

  • Run some code bigger than one line without a temporary file

  • Play around with libraries and modules

  • You can even call a console in your script and play around in script's context

For Ruby it would be irb, for Python is... python byitself and for perl... and there was nothing for perl (except that ugly perl -d -e "" and several failed projects) until Devel::REPL was written by Matt S Trout (a.k.a. mst) from ShadowCatSystems http://www.shadowcatsystems.co.uk.

Devel::REPL - the Perl console

REPL stands for Read, Evaluate, Print, Loop. Lets install and try it.

$ cpan Devel::REPL

After installation you have a lot of new modules, but the most interesting things are:

  • Devel::REPL A top level module.

  • re.pl Wrapper script, running console.

And a bunch of plugins (I'll describe them later). In command line type:

$ re.pl

If everything is ok you'll see a prompt (underlined $). That's it. You can start typing expressions.

An example session:

$ sub factorial {

> my $number = shift;

> return $number > 1 ? $number * factorial($number-1) : $number;

> }

$ factorial 1 # by the way, comments are allowed

1 # our return value

$ factorial 5

120

$ [1,2,3,4,5,6,7]
$ARRAY1 = [
            1,
            2,
            3, # return values are printed with Data::Dumper::Streamer.
            4, # See Plugins section
            5,
            6,
            7
          ];

$ {apple=>1,fruit=>'apple',cart=>['apple','banana']}
$HASH1 = {
          apple => 1,
          cart  => [
                    'apple',
                    'banana'
          ],
          fruit => 'apple'
};

$ package MyPackage; # create a package

$ sub say_hi { # define a sub

> print "Hi!\n";

> } # statement is evaluated only after we've finished typing block.
    # See Plugins section.
> __PACKAGE__
MyPackage
> package main;

> __PACKAGE_
main
> MyPackage->say_hi
Hi!
1
$

Control files a.k.a. I don't want to type it every time

Devel::REPL has control files feature. Control files are evaluated on session start in the same way as you would type them manually in console.

Default control file is located at `$HOME/.re.pl/repl.rc` .

You can store there any statements you would normally type in.

I.e. my `$HOME/.re.pl/repl.rc` has next lines:

use feature 'say'; # to don't write \n all the time

use Data::Dumper;

# pretty print data structures
sub pp { print Data::Dumper->Dump([@_]) }

You can have multiple control files and they can be anywhere in the file system. To make re.pl use some rc-file other than repl.rc call it like this:

$ re.pl --rcfile /path/to/your/rc.file

If your rc-file is in `$HOME/.re.pl` directory, you can omit path:

$ re.pl --rcfile rc.file

If you have rc-file with the same name in current directory and you don't want to type path, you can:

$ re.pl --rcfile ./rc.file

I want it to bark, fly, jump and swim! or Plugins

Plugins extend functionality and change behavor of Devel::REPL. Bundled plugins are:

  • Devel::REPL::Plugin::History No comments. Simply history.

  • Devel::REPL::Plugin::!LexEnv Provides a lexical environment for the Devel::REPL.

  • Devel::REPL::Plugin::DDS Formats return values with Data::Dump::Streamer module.

  • Devel::REPL::Plugin::Packages Keeps track of which package your're in.

  • Devel::REPL::Plugin::Commands Generic command creation plugin using injected functions.

  • Devel::REPL::Plugin::MultiLine::PPI Makes Devel::REPL read your input until your block is finished. What does this means: you can type a part of a block on one line and second part on another:

         $ sub mysub {

     > print "Hello, World!\n"; ## notice prompt change

     > }

     $ mysub
     Hello, World!
     1
     $

but this *doesn't* mean you can print sub name or identifier
on several lines. Don't do that! It won't work.

There are lots of contributed plugins you can find at CPAN.

Profiles

If plugins change and extend functionality of Devel::REPL, profiles are changing your environment (loaded plugins, constants, subs and etc.).

There's only one bundled profile called `Devel::REPL::Profile::Default`, lets take a look at it:

      package Devel::REPL::Profile::Default;

      use Moose; ### advanced OOP system for Perl

      ### keep those exports/imports out of our namespace
      use namespace::autoclean;

      with 'Devel::REPL::Profile';  ## seem perldoc Muse

      sub plugins { ### plugins we want to be loaded
        qw(History LexEnv DDS Packages Commands MultiLine::PPI);
      }

      ### the only required sub for profile,
      ### it is called on profile activation
      sub apply_profile {
        my ($self, $repl) = @_;
	### $self - no comments, $repl - current instance of Devel::REPL

        $repl->load_plugin($_) for $self->plugins; ### load our plugins
      }

      1;

At the moment there are no profiles on CPAN. Mostly you'll use control files. To enable some profile use --profile switch:

$ re.pl --profile SomeProfile

See Also

Devel::REPL, Devel::REPL::Plugin, Devel::REPL::Profile