This is doc/epl.info, produced by makeinfo version 4.0 from
doc/epl.texi.

INFO-DIR-SECTION Emacs
START-INFO-DIR-ENTRY
* EPL: (epl).           Script Emacs with Perl.
END-INFO-DIR-ENTRY

   This Info file documents EPL, an Emacs extension that supports the
use of Perl to write other Emacs extensions.

   Copyright (C) 2001 John Tobey <jtobey@john-edwin-tobey.org>

   This edition is for EPL version 0.7, 13 January 2001.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover texts, and no Back-Cover Texts.  A
copy of the license is included in the section entitled "GNU Free
Documentation License".


File: epl.info,  Node: Top,  Next: Preface,  Up: (dir)

EPL
***

   This is edition 0.2 of the EPL Reference Manual, corresponding to
EPL version 0.7.

   EPL (Emacs Perl) is a library of Lisp functions and Perl modules that
let you write Emacs extensions in Perl.

* Menu:

* Preface::                     Why I'm here.
* Introduction::                Beginning with an example.
* Features::                    How Perl looks to Lisp, how Lisp looks to Perl.
* Configuration::               Changing the defaults.
* Internals::                   What happens under the hood.

Appendices

* Copying Conditions::          The GNU Free Documentation License.
* Index::                       Index to this manual.


 --- The Detailed Node Listing ---

Introduction to EPL

* Perl Example::                An example: Find files containing regex.
* History::                     EPL uses IPC, not translation or embedding.
* Emacs Lisp::                  You need the Emacs Lisp Reference Manual.
* Coding Conventions::          Why the Perl examples use `&FUNCTION()'.

How Language Features Correspond

* Data Conversion::             Working with each other's data types.
* Functions::                   Transfering program control.
* Control Structures::          Exceptions; `throw', `signal', `die'.
* Input/Output::                Perl's primitives are redefined in Emacs.
* Caveats::                     It's not always a happy marriage.

Configuration

* Installation::                Lisp files, Perl modules, documentation.
* The Easy Way::                We like the defaults.
* Starting a Perl Process in Emacs::   `make-perl-interpreter'.
* Starting an Emacs Process in Perl::  `use Emacs;'.

Internals

* Debugging Options::           Dumping traffic to stderr or a buffer.
* Transport Layer::             Media of interprocess communication.
* Message Types::               What interpreters can say to each other.
* State Transitions::           The message stream grammar.
* Protocol::                    Current EPL protocol (*subject to change*).


File: epl.info,  Node: Preface,  Next: Introduction,  Prev: Top,  Up: Top

Preface
*******

   Like a lot of people, I learned Perl because of the Web.  I came to
GNU from a Microsoft background early in 1996, when Microsoft had only
begun to realize that the Internet was hot.  I was deeply infused with
Web hype, willing to try something different, and aware that the Web
ran on Unix and Perl.

   I came to Emacs because of genetic predisposition.  A tightly
integrated, yet versatile, complex system with endless opportunities
for learning and automation helps reduce my cholesterol and, I think,
aids respiration and digestion.  It had all the good features of
Microsoft Office, without all the headaches and nausea.

   Well, it had _almost_ all the good features.

   Emacs is an oasis of integration in the chaotic and disparate realm
of Linux and Unix.  (I later learned that the Unix kernel is a thing of
some elegance, but at the level of `/etc/resolv.conf', X11R6, and
`~/.fvwmrc', there was little cohesion.)  As I entered this realm, it
irked me that I had to learn _two_ scripting languages to do what I
wanted, whereas Visual Basic, clunky as it is, does everything on
Windows.

   Speaking of that other--umm--language, Visual Basic shares an
important feature with Perl: It is for ordinary people.

   Now, I am very glad that Emacs lets you do just about anything with
Elisp (such as write EPL).  But my conceptual mapping from Windows onto
Unix paired Visual Basic with Perl, not Lisp, as the general workhorse
get-it-done tool.  It seemed to me not right that the standard,
full-featured editor on my new system could not understand the
standard, full-featured scripting language.  With EPL--Emacs PerL, or
Emacs-Perl-Lisp--I hope to rectify the situation.


File: epl.info,  Node: Introduction,  Next: Features,  Prev: Preface,  Up: Top

Introduction
************

   EPL is an extension for GNU Emacs
(http://www.gnu.org/software/emacs/) and XEmacs (http://www.xemacs.org)
that lets you write commands in Perl.  It is also a programming
interface for Elisp (*note Emacs Lisp::) programs to use Perl features
and an interface for Perl to use Emacs.

   This document assumes knowledge of Emacs terms such as "the
minibuffer" and "`M-x'" (*note Running Commands by Name: (emacs)Top.).
It assumes knowledge of Perl references and nested data structures
(perlref(1)), and packages and modules (perlmod(1)).

* Menu:

* Perl Example::                An example: Find files containing regex.
* History::                     EPL uses IPC, not translation or embedding.
* Emacs Lisp::                  You need the Emacs Lisp Reference Manual.
* Coding Conventions::          Why the Perl examples use `&FUNCTION()'.


File: epl.info,  Node: Perl Example,  Next: History,  Up: Introduction

Perl Example
============

   Let's illustrate EPL with an example.  Suppose you often want to edit
many files in the same directory based on some text that they contain.
You want a command that will look for a specified regular expression in
each file, and if found, open the file in a buffer.  You prefer Perl
regular expressions to Emacs ones, and you are not interested in files
that Perl considers to be binary.

   Here is some Emacs Perl code that will do it:

     use IO::Dir;
     use IO::File;
     
     sub find_my_files ($$) {
         my ($dirname, $regex) = @_;
     
         # Convert "~" to home dir.
         $dirname = &expand_file_name ($dirname);
     
         my $dh = IO::Dir->new ($dirname)
             or die "$dirname: $!";
     
         my $count = 0;
         while (defined ($filename = $dh->read)) {
             $filename = "$dirname/$filename";
     
             # Skip directories and binary files.
             next unless -f($filename) && -T($filename);
     
             my $fh = IO::File->new ($filename);
             if (!$fh) {
                 warn ("$filename: $!");
                 next;
             }
             while (defined ($_ = <$fh>)) {
                 if (/$regex/) {
                     &find_file($filename);
                     $count++;
                     last;
                 }
             }
         }
         &message ("Found $regex in $count file(s)");
     }
     
     defun (\*find_files_containing_regex,
            "Open all files whose contents match a Perl regular expression.",
            interactive("DLook in directory: \nsPerl regex: "),
            \&find_my_files);

   You would save this in a file, load it with `M-x perl-load-file'
(*note Evaluation::) or from `~/.emacs', and use it as `M-x
find-files-containing-regex'.

   The command prompts for a directory name (with <TAB>-completion and
history) and an arbitrary string (regex).  It signals an error if it
can't read the directory, and otherwise summarizes the results in the
minibuffer.  You can access its documentation just like that of any
Emacs command, using `C-h f find-files-containing-regex'.


File: epl.info,  Node: History,  Next: Emacs Lisp,  Prev: Perl Example,  Up: Introduction

History
=======

   EPL works by starting a subprocess the first time a Perl interpreter
is needed to carry out some function.  Emacs and Perl use interprocess
communication (IPC) to invoke functions and send each other data until
the parent process terminates.  Variations on this theme may involve
Perl as the parent process or more than one child per parent.

   This is not the only possible implementation.  In principle, the same
functionality could be achieved by translating Perl to Lisp.  That has
been a goal of the GNU project since 1994, except that RMS wants to
replace Elisp with Scheme first.  For details, see *Note Lisp History:
(elisp)Lisp History, and `http://www.vanderburg.org/Tcl/war/'.

   Another possibility, which has been realized by a program called
Perlmacs (http://john-edwin-tobey.org/perlmacs/), is to embed the Perl
interpreter in Emacs and let it operate directly at the C level the way
the Elisp interpreter does.  This probably results in faster execution,
but it ties an executable to specific versions of Perl and Emacs.
Perlmacs does not support XEmacs.


File: epl.info,  Node: Emacs Lisp,  Next: Coding Conventions,  Prev: History,  Up: Introduction

Emacs Lisp
==========

   Whether you write EPL programs or Elisp programs, you are writing
Emacs programs.  The GNU and XEmacs projects maintain comprehensive and
thorough documentation of the functions available to Emacs extensions.

   Of course, those documents assume that extensions use Lisp.  Still,
they are an invaluable resource, and any programmer with a general
understanding of functions and variables can make good use of them.
This manual makes frequent reference to the *Note GNU Emacs Lisp
Reference Manual: (elisp)Top.  If you don't have it, go get it!  It
should be available wherever you got Emacs or from the Free Software
Foundation (http://www.gnu.org/doc/doc.html).

   Who knows?  You may fall in love with Lisp.


File: epl.info,  Node: Coding Conventions,  Prev: Emacs Lisp,  Up: Introduction

Coding Conventions
==================


File: epl.info,  Node: Features,  Next: Configuration,  Prev: Introduction,  Up: Top

Features
********

   This chapter describes EPL's mapping between Perl's language features
and Emacs Lisp's.  Perl and Lisp are quite different, so some features
favored by one language are imperfectly or awkwardly reproduced in the
other.  EPL follows Perl's philosophy of making simple things easy and
hard things possible.

* Menu:

* Data Conversion::             Working with each other's data types.
* Functions::                   Calling each other's functions, `defun'.
* Control Structures::          Exceptions; `throw', `signal', `die'.
* Input/Output::                Perl's primitives are redefined in Emacs.
* Caveats::                     It's not always a happy marriage.


File: epl.info,  Node: Data Conversion,  Next: Functions,  Up: Features

Data Conversion
===============

   EPL provides essentially two mechanisms to transfer data between
languages--as function arguments and return values.  In both cases,
data may be passed either by value or by reference.  The default is by
value, since references incur overhead (*note References Incur
Overhead::).

   In EPL, "by value" means recursively (or "deeply") copied.  That is,
containers in the originating language are converted to analogous
containers in the destination language, and any contained elements not
explicitly marked as pass-by-reference are likewise converted.  This
allows the recipient to examine a structure using its built-in
accessors, but changes will not apply to the original.  Also, language
peculiarities result in information loss during some conversions, so
pass-by-value is not completely reversible (*note Conversion Is
Imperfect::).

   This section describes the conversions that apply to each language's
scalar and container types.  For a complete description of Lisp types,
see *Note Lisp Data Types: (elisp)Lisp Data Types.

* Menu:

* Scalars::                     Lisp has three scalar types.
* The Null Value::              `undef' and `()' are `nil'.
* Symbols and Globrefs::        `\*::sym' is `'sym'.
* Lists and Arrayrefs::         `["fnord"]' is `'("fnord")'.
* Vectors::                     `\[42]' is `[42]'.
* Conses::                      The `Emacs::Lisp::Cons' type.
* Scalar References::           The `perl-ref' type.
* Code References::             `\&frob' is a lambda expression.
* Hash Tables::                 Not yet implemented.
* Blessed References::          Not yet implemented.
* Emacs Types::                 Not yet implemented.


File: epl.info,  Node: Scalars,  Next: The Null Value,  Up: Data Conversion

Scalars
-------

   Lisp integers, floats, and strings all become Perl scalars.  A simple
Perl scalar becomes either an integer, a float, or a string.

   Unfortunately, it is hard to be certain which type will be chosen.
It depends on the value.  Perl 5.005 and later can distinguish among the
literal constants `1', `"1"', and `1.0', and EPL uses this information.
However, not all Perl integers fit into an Emacs integer (which is 28
bits, *note Integer Type: (elisp)Integer Type.).  Integers that would
overflow are upgraded to floats when converted.

   You _may_ be able to specify string conversion by wrapping a
variable in double quotes (`"$var"'), float by adding zero (`$var +
0'), and integer using (`int($var)').  Perhaps a future version of EPL
will provide an explicit means of specification.

   Interesting character encodings such as UTF-8 are not currently
supported.  All strings are considered unibyte.  *Note Text
Representations: (elisp)Text Representations.


File: epl.info,  Node: The Null Value,  Next: Symbols and Globrefs,  Prev: Scalars,  Up: Data Conversion

The Null Value
--------------

   As an exception to the rule for symbols (*note Symbols and
Globrefs::), `nil' in Lisp corresponds to `undef' in Perl.

   In Lisp, `nil' is really a symbol.  However, it is typically used as
the boolean value FALSE.  Perl symbols (glob references) evaluate to
TRUE in boolean context.  It is very natural to convert `nil' to
`undef'.


File: epl.info,  Node: Symbols and Globrefs,  Next: Lists and Arrayrefs,  Prev: The Null Value,  Up: Data Conversion

Symbols and Globrefs
--------------------

   Glob references become symbols in Lisp.  Underscores are swapped with
hyphens in the name, since Perl prefers underscores and Lisp prefers
hyphens.


File: epl.info,  Node: Lists and Arrayrefs,  Next: Vectors,  Prev: Symbols and Globrefs,  Up: Data Conversion

Lists and Arrayrefs
-------------------

   Lists are a central data structure in Lisp.  To make it as easy as
possible to pass lists to Lisp functions that require them, Perl array
references are converted Lisp lists.  For example, the Perl expression

     ["x", ["y", 1]]
   is converted to
     '("x" ("y" 1))

   in Lisp.  Note, however, that the empty list in Lisp is
indistinguishable from `nil', so it becomes the undefined value, not an
arrayref.  *Note The Null Value::.


File: epl.info,  Node: Vectors,  Next: Conses,  Prev: Lists and Arrayrefs,  Up: Data Conversion

Vectors
-------

   Adding `\' to an arrayref makes it an arrayref ref, which EPL treats
as a vector in Lisp.  For example, Perl `\[1, 2, []]' becomes Lisp `[1
2 nil]'.


File: epl.info,  Node: Conses,  Next: Scalar References,  Prev: Vectors,  Up: Data Conversion

Conses
------

   Conses that are not lists become Emacs::Lisp::Cons objects.

   *Compatibility note:*  In Perlmacs, such conses become opaque
objects (*note Pass-by-Reference::).

     $x = &cons("left", "right");
     print ref($x);                # "Emacs::Lisp::Cons"
     print $x->car;                # "left"
     print $x->cdr;                # "right"
   But:
     $x = &cons ("top", undef);    # a Lisp list
     print ref($x);                # "ARRAY"
     print $x->[0];                # "top"


File: epl.info,  Node: Scalar References,  Next: Code References,  Prev: Conses,  Up: Data Conversion

Scalar References
-----------------


File: epl.info,  Node: Code References,  Next: Hash Tables,  Prev: Scalar References,  Up: Data Conversion

Code References
---------------


File: epl.info,  Node: Hash Tables,  Next: Blessed References,  Prev: Code References,  Up: Data Conversion

Hash Tables
-----------

   The issue with hash tables is that Perl's built-in ones permit only
string keys.  Right now, hash tables are passed by reference (*note
Pass-by-Reference::).


File: epl.info,  Node: Blessed References,  Next: Emacs Types,  Prev: Hash Tables,  Up: Data Conversion

Blessed References
------------------


File: epl.info,  Node: Emacs Types,  Prev: Blessed References,  Up: Data Conversion

Emacs Types
-----------


File: epl.info,  Node: Functions,  Next: Control Structures,  Prev: Data Conversion,  Up: Features

Functions
=========

* Menu:

* Evaluation::                  `perl-eval'.
* Ordinary Functions::          `perl-call', `use Emacs::Lisp;'.
* Pass-by-Reference::           How to inhibit data conversion.
* Commands::                    Extending Emacs without Lisp, `defun'.


File: epl.info,  Node: Evaluation,  Next: Ordinary Functions,  Up: Functions

Evaluation
----------

 - Function: perl-eval string &optional context
     This function parses and executes STRING as Perl code and returns
     its converted value (*note Data Conversion::).

     CONTEXT can specify an evaluation context (see perlsub
     documentation (http://www.perldoc.org)) and affects how the
     results are returned.  It may be:

    `scalar-context'
          Evaluate in scalar context and return the result as a Lisp
          object.  This is the default if CONTEXT is not given.

    `list-context'
          Evaluate in list context and return the result as a list.

    `void-context'
          Evaluate in void context and return `nil'.

 - Function: perl-eval-raw string &optional context
     This function executes STRING like `perl-eval' but does not
     convert its value.  Instead, it returns a `perl-value' object that
     keeps a reference to a value in Perl.


File: epl.info,  Node: Ordinary Functions,  Next: Pass-by-Reference,  Prev: Evaluation,  Up: Functions

Ordinary Functions
------------------

 - Function: perl-call sub &rest arguments
     This function calls the Perl subroutine named SUB with ARGUMENTS
     and returns its value.  If the first argument is `scalar-context',
     `list-context', or `void-context', it is not passed to the sub but
     affects the calling context as in `perl-eval'.  *Note Evaluation::.


File: epl.info,  Node: Pass-by-Reference,  Next: Commands,  Prev: Ordinary Functions,  Up: Functions

Pass-by-Reference
-----------------

   XXX Rewrite.

   A "shallow copy" simply wraps a Perl scalar in a Lisp object or vice
versa.  Wrapped Perl values appear as a Lisp objects of type
`perl-value'.  Wrapped Lisp values appear in Perl as objects of class
`Emacs::Lisp::Object'.  *Note References Incur Overhead::, for issues
relating to wrapped data.

   In Perl, the `wrap' function wraps its argument in a Lisp object.
This allows Perl data such as arrays to be passed by reference to Lisp
functions.  Another way Lisp can obtain references to Perl data is by
using `perl-eval-raw' or `perl-call-raw'.  Lisp can tell whether an
object refers to Perl data by using the `perl-value-p' function.

   Of course, `wrap' is a Perl function, so the value it returns is
really its argument wrapped in a Lisp object wrapped in a Perl object.
But when you pass this object to Lisp as an argument or function return
value, Lisp gets a reference to the original object, and no automatic
conversion occurs.  Lisp may explicitly convert it at any time using
the `perl-to-lisp' function, and any changes made by Perl will be
visible at the time of conversion.

   The Lisp function `perl-wrap' is the counterpart of Perl's `wrap'
function, and the `Emacs::Lisp::Object' package provides the equivalent
of `perl-call-raw'.  The functions of package `Emacs::Lisp' return deep
copies of Lisp function return values (see *note Functions::).
However, the corresponding `Emacs::Lisp::Object' functions return
references to live Lisp objects.

   Since a wrapped Lisp object appears in Perl as an
`Emacs::Lisp::Object' blessed reference, if follows that it can be used
with method syntax to invoke a function and pass itself as the first
argument.  Thus, supposing `v' is a vector of conses and `$v' is its
wrapper, this Perl code

     $v->aref(3)->setcdr(t);
   has the effect of the following Lisp:
     (setcdr (aref v 3) t)

   An Emacs::Lisp::Object's `to_perl' method performs a deep copy and
is the counterpart of `perl-to-lisp'.

   Lisp functions called through package Emacs::Lisp convert their
return values using deep copying.  The same functions are accessible
through Emacs::Lisp::Object, which does shallow conversion and always
returns an Emacs::Lisp::Object object.

   These examples show how the data wrapping functions work in Perl:

     $x = wrap [1, 2, 3];
     print ref($x);           # "Emacs::Lisp::Object"
     print ref($x->to_perl);  # "ARRAY"
     print @{&list(2, 3)};    # "23"
     
     $x = Emacs::Lisp::Object::list(2, 3);
     print ref($x);           # "Emacs::Lisp::Object"
     print @{$x->to_perl};    # "23"

   And in Lisp:

     XXX


File: epl.info,  Node: Commands,  Prev: Pass-by-Reference,  Up: Functions

Commands
--------


File: epl.info,  Node: Control Structures,  Next: Input/Output,  Prev: Functions,  Up: Features

Control Structures
==================


File: epl.info,  Node: Input/Output,  Next: Caveats,  Prev: Control Structures,  Up: Features

Input/Output
============


File: epl.info,  Node: Caveats,  Prev: Input/Output,  Up: Features

Caveats
=======

* Menu:

* References Incur Overhead::   Memory management hurdles.
* Conversion Is Imperfect::     Natural mappings are not always 1-to-1.


File: epl.info,  Node: References Incur Overhead,  Next: Conversion Is Imperfect,  Up: Caveats

References Incur Overhead
-------------------------


File: epl.info,  Node: Conversion Is Imperfect,  Prev: References Incur Overhead,  Up: Caveats

Conversion Is Imperfect
-----------------------


File: epl.info,  Node: Configuration,  Next: Internals,  Prev: Features,  Up: Top

Configuration
*************

* Menu:

* Installation::                Lisp files, Perl modules, documentation.
* The Easy Way::                We like the defaults.
* Starting a Perl Process in Emacs::   `make-perl-interpreter'.
* Starting an Emacs Process in Perl::  `use Emacs::Lisp;'.


File: epl.info,  Node: Installation,  Next: The Easy Way,  Up: Configuration

Installation
============


File: epl.info,  Node: The Easy Way,  Next: Starting a Perl Process in Emacs,  Prev: Installation,  Up: Configuration

The Easy Way
============


File: epl.info,  Node: Starting a Perl Process in Emacs,  Next: Starting an Emacs Process in Perl,  Prev: The Easy Way,  Up: Configuration

Starting a Perl Process in Emacs
================================


File: epl.info,  Node: Starting an Emacs Process in Perl,  Prev: Starting a Perl Process in Emacs,  Up: Configuration

Starting an Emacs Process in Perl
=================================


File: epl.info,  Node: Internals,  Next: Copying Conditions,  Prev: Configuration,  Up: Top

Internals
*********

   This chapter introduces the concepts involved in supporting
single-threaded distributed exception handling and garbage collection
for languages like Perl and Emacs Lisp.  These languages have a lot
more in common underneath than meets the eye.

   The chapter ends with a more concrete description of EPL's protocol.
This information changes with great frequency and may be completely
outdated by the time you read this.

* Menu:

* Debugging Options::           Dumping traffic to stderr or a buffer.
* Transport Layer::             Media of interprocess communication.
* Message Types::               What interpreters can say to each other.
* State Transitions::           The message stream grammar.
* Protocol::                    Current EPL protocol (*subject to change*).


File: epl.info,  Node: Debugging Options,  Next: Transport Layer,  Up: Internals

Debugging Options
=================

   You can make either or both processes log the messages sent between
them.

 - Perl Variable: $Emacs::EPL::debugging
     When this variable holds a true value, the Perl side of EPL logs
     messages to and from Emacs.  Possible values are:

    `"stderr"'
          Send debugging output to `STDERR'.  This works only when Perl
          is the parent process.

    a string
          Append debugging output to the file named by the string.

    a scalar reference
          Append debugging output to the scalar.  This requires the
          IO::Scalar module.

    a filehandle
          Print debugging output to the handle.

 - Perl Function: Emacs::EPL::debug string...
     This is the function used internally to send debugging output to
     the destination specified by `$Emacs::EPL::debugging'.

 - Variable: epl-debugging
     When this variable's value is non-`nil', the Emacs side of EPL
     logs messages to and from Perl.  If it is the symbol `stderr', the
     output goes to the standard error stream.  Otherwise, it goes to a
     buffer named `*epl-debug*'.

     The log messages include the exact text sent to Perl, but the
     replies are printed as Lisp forms using `prin1'.  However, EPL
     always uses a buffer named `*perl*' to receive text from Perl.
     Normally, it erases this buffer after every message, but when
     `epl-debugging' is true, it does not.

 - Function: epl-debug &rest objects
     This is the function used internally to send output to the location
     specified by `epl-debugging'.


File: epl.info,  Node: Transport Layer,  Next: Message Types,  Prev: Debugging Options,  Up: Internals

Transport Layer
===============


File: epl.info,  Node: Message Types,  Next: State Transitions,  Prev: Transport Layer,  Up: Internals

Message Types
=============


File: epl.info,  Node: State Transitions,  Next: Protocol,  Prev: Message Types,  Up: Internals

State Transitions
=================


File: epl.info,  Node: Protocol,  Prev: State Transitions,  Up: Internals

Protocol
========


File: epl.info,  Node: Copying Conditions,  Next: Index,  Prev: Internals,  Up: Top

Copying Conditions
******************

   You are welcome to distribute EPL under the terms of either the Perl
Artistic License (as distributed with Perl 5.6.0) or the GNU General
Public License.

     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU General Public License as
     published by the Free Software Foundation; either version 2, or
     (at your option) any later version.

     This software 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.  See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this library; see the file COPYING.  If not, write to
     the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
     Boston, MA 02111-1307, USA.

   You may distribute copies of this documentation in accordance with
the *Note GNU Free Documentation License::, Version 1.1 or any later
version published by the Free Software Foundation; with no required
Invariant Sections, Front-Cover texts, or Back-Cover Texts.

* Menu:

* GNU Free Documentation License::    The GNU FDL.


File: epl.info,  Node: GNU Free Documentation License,  Up: Copying Conditions

GNU Free Documentation License
==============================

                        Version 1.1, March 2000

     Copyright (C) 2000 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA  02111-1307, USA
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     written document "free" in the sense of freedom: to assure everyone
     the effective freedom to copy and redistribute it, with or without
     modifying it, either commercially or noncommercially.  Secondarily,
     this License preserves for the author and publisher a way to get
     credit for their work, while not being considered responsible for
     modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.
     We recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work that contains a
     notice placed by the copyright holder saying it can be distributed
     under the terms of this License.  The "Document", below, refers to
     any such manual or work.  Any member of the public is a licensee,
     and is addressed as "you".

     A "Modified Version" of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A "Secondary Section" is a named appendix or a front-matter
     section of the Document that deals exclusively with the
     relationship of the publishers or authors of the Document to the
     Document's overall subject (or to related matters) and contains
     nothing that could fall directly within that overall subject.
     (For example, if the Document is in part a textbook of
     mathematics, a Secondary Section may not explain any mathematics.)
     The relationship could be a matter of historical connection with
     the subject or with related matters, or of legal, commercial,
     philosophical, ethical or political position regarding them.

     The "Invariant Sections" are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in
     the notice that says that the Document is released under this
     License.

     The "Cover Texts" are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.

     A "Transparent" copy of the Document means a machine-readable copy,
     represented in a format whose specification is available to the
     general public, whose contents can be viewed and edited directly
     and straightforwardly with generic text editors or (for images
     composed of pixels) generic paint programs or (for drawings) some
     widely available drawing editor, and that is suitable for input to
     text formatters or for automatic translation to a variety of
     formats suitable for input to text formatters.  A copy made in an
     otherwise Transparent file format whose markup has been designed
     to thwart or discourage subsequent modification by readers is not
     Transparent.  A copy that is not "Transparent" is called "Opaque".

     Examples of suitable formats for Transparent copies include plain
     ASCII without markup, Texinfo input format, LaTeX input format,
     SGML or XML using a publicly available DTD, and
     standard-conforming simple HTML designed for human modification.
     Opaque formats include PostScript, PDF, proprietary formats that
     can be read and edited only by proprietary word processors, SGML
     or XML for which the DTD and/or processing tools are not generally
     available, and the machine-generated HTML produced by some word
     processors for output purposes only.

     The "Title Page" means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, "Title
     Page" means the text near the most prominent appearance of the
     work's title, preceding the beginning of the body of the text.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow
     the conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies of the Document numbering more than
     100, and the Document's license notice requires Cover Texts, you
     must enclose the copies in covers that carry, clearly and legibly,
     all these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the
     title equally prominent and visible.  You may add other material
     on the covers in addition.  Copying with changes limited to the
     covers, as long as they preserve the title of the Document and
     satisfy these conditions, can be treated as verbatim copying in
     other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a
     machine-readable Transparent copy along with each Opaque copy, or
     state in or with each Opaque copy a publicly-accessible
     computer-network location containing a complete Transparent copy
     of the Document, free of added material, which the general
     network-using public has access to download anonymously at no
     charge using public-standard network protocols.  If you use the
     latter option, you must take reasonably prudent steps, when you
     begin distribution of Opaque copies in quantity, to ensure that
     this Transparent copy will remain thus accessible at the stated
     location until at least one year after the last time you
     distribute an Opaque copy (directly or through your agents or
     retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of
     copies, to give them a chance to provide you with an updated
     version of the Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with
     the Modified Version filling the role of the Document, thus
     licensing distribution and modification of the Modified Version to
     whoever possesses a copy of it.  In addition, you must do these
     things in the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of
          previous versions (which should, if there were any, be listed
          in the History section of the Document).  You may use the
          same title as a previous version if the original publisher of
          that version gives permission.

       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has less than five).

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section entitled "History", and its title, and
          add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on
          the Title Page.  If there is no section entitled "History" in
          the Document, create one stating the title, year, authors,
          and publisher of the Document as given on its Title Page,
          then add an item describing the Modified Version as stated in
          the previous sentence.

       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in
          the "History" section.  You may omit a network location for a
          work that was published at least four years before the
          Document itself, or if the original publisher of the version
          it refers to gives permission.

       K. In any section entitled "Acknowledgments" or "Dedications",
          preserve the section's title, and preserve in the section all
          the substance and tone of each of the contributor
          acknowledgments and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document,
          unaltered in their text and in their titles.  Section numbers
          or the equivalent are not considered part of the section
          titles.

       M. Delete any section entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section as "Endorsements" or to
          conflict in title with any Invariant Section.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option
     designate some or all of these sections as invariant.  To do this,
     add their titles to the list of Invariant Sections in the Modified
     Version's license notice.  These titles must be distinct from any
     other section titles.

     You may add a section entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties--for example, statements of peer review or that the text
     has been approved by an organization as the authoritative
     definition of a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end
     of the list of Cover Texts in the Modified Version.  Only one
     passage of Front-Cover Text and one of Back-Cover Text may be
     added by (or through arrangements made by) any one entity.  If the
     Document already includes a cover text for the same cover,
     previously added by you or by arrangement made by the same entity
     you are acting on behalf of, you may not add another; but you may
     replace the old one, on explicit permission from the previous
     publisher that added the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination
     all of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections entitled
     "History" in the various original documents, forming one section
     entitled "History"; likewise combine any sections entitled
     "Acknowledgments", and any sections entitled "Dedications".  You
     must delete all sections entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the
     documents in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow
     this License in all other respects regarding verbatim copying of
     that document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of
     a storage or distribution medium, does not as a whole count as a
     Modified Version of the Document, provided no compilation
     copyright is claimed for the compilation.  Such a compilation is
     called an "aggregate", and this License does not apply to the
     other self-contained works thus compiled with the Document, on
     account of their being thus compiled, if they are not themselves
     derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one
     quarter of the entire aggregate, the Document's Cover Texts may be
     placed on covers that surround only the Document within the
     aggregate.  Otherwise they must appear on covers around the whole
     aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License provided that you also include the
     original English version of this License.  In case of a
     disagreement between the translation and the original English
     version of this License, the original English version will prevail.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided for under this License.  Any other
     attempt to copy, modify, sublicense or distribute the Document is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     `http://www.gnu.org/copyleft/'.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If
     the Document does not specify a version number of this License,
     you may choose any version ever published (not as a draft) by the
     Free Software Foundation.

ADDENDUM: How to use this License for your documents
----------------------------------------------------

   To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.1
       or any later version published by the Free Software Foundation;
       with the Invariant Sections being LIST THEIR TITLES, with the
       Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
       A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have no Invariant Sections, write "with no Invariant Sections"
instead of saying which ones are invariant.  If you have no Front-Cover
Texts, write "no Front-Cover Texts" instead of "Front-Cover Texts being
LIST"; likewise for Back-Cover Texts.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.


File: epl.info,  Node: Index,  Prev: Copying Conditions,  Up: Top

Index
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* Menu:

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Tag Table:
Node: Top798
Node: Preface2864
Node: Introduction4645
Node: Perl Example5600
Node: History7831
Node: Emacs Lisp9018
Node: Coding Conventions9856
Node: Features9978
Node: Data Conversion10757
Node: Scalars12539
Node: The Null Value13601
Node: Symbols and Globrefs14078
Node: Lists and Arrayrefs14393
Node: Vectors14988
Node: Conses15257
Node: Scalar References15862
Node: Code References16004
Node: Hash Tables16147
Node: Blessed References16445
Node: Emacs Types16591
Node: Functions16703
Node: Evaluation17081
Node: Ordinary Functions18070
Node: Pass-by-Reference18546
Node: Commands21312
Node: Control Structures21408
Node: Input/Output21546
Node: Caveats21670
Node: References Incur Overhead21898
Node: Conversion Is Imperfect22049
Node: Configuration22196
Node: Installation22570
Node: The Easy Way22677
Node: Starting a Perl Process in Emacs22825
Node: Starting an Emacs Process in Perl23034
Node: Internals23224
Node: Debugging Options24124
Node: Transport Layer25789
Node: Message Types25928
Node: State Transitions26063
Node: Protocol26199
Node: Copying Conditions26295
Node: GNU Free Documentation License27655
Node: Index47518

End Tag Table
