Copyright 1998, O'Reilly & Associates, Inc.

This package may be copied under the same terms as Perl itself.

Disclaimers
-----------
This is a work in progress, and relies on bleeding-edge technology
from the network.  Don't expect not to be surprised occasionally.

Requirements
------------
Under Solaris and Linux (and other Unix-like systems), Perl 5.005 (or later)
must be compiled and installed as a shared library (libperl.so).  I had to use
the system's malloc.  JPL was originally built and tested with 5.004_04 and
early Java 1.1 development kits.  This version has not been well tested under
other versions, so you can expect some rough edges.

You need JDK 1.1.  On Solaris, 1.1.5 has been verified to work.  Linux
users can try the latest version (1.1.3 or later) available from (for
example):

  ftp://ftp.blackdown.org/pub/Linux/JDK/1.1.3/updates/libjava-1.1.3v2-1.tar.gz

The get_jdk directory contains a script that will download JDK (but not
the patch file above) off of the net for you.  (This presumes you've
already installed the modules mentioned in ../README.)

You may need to ensure that all files under the ../jpl directory are writable.
install-jpl expects to be run with super-user privileges so that it can
put things in the right places.

Microsoft Windows
-----------------
Only a subset of JPL works under Microsoft Windows.  This subset includes
the JNI extension and the JPL module.  This is enough for you to embed
Java in Perl, but not Perl in Java.

This has only been tested with the Sun JDK 1.1.8. I haven't tested it
with JDK 1.2 (aka Java 2) or any Microsoft implementation of Java.

Kaffe
-----
You might notice some mention of Kaffe (www.kaffe.org) in the source files. 
This is because some preliminary work is being done in this area, but JPL
doesn't yet work with Kaffe.

What the heck is JPL?
---------------------
JPL is a hybrid (to use the polite term) language.  It's basically Java
in which the methods can optionally be implemented by Perl code.  A
preprocessor called "JPL::Compile" looks at your .jpl file and spits
out the appropriate .java, .c, .h, .pl, and .so files to accomplish the
desired task.  Hopefully a lot of those files can go away in the future
as jpl mutates into a Perl-to-Java compiler.  The long-term goal is for
jpl to be able to take a pure Perl file and spit out a java .class
file.  This initial version of JPL is an attempt to begin to mesh the
semantics of Java and Perl.  Some people may find it useful in its
current form, but you should know right up front that we've still got a
ways to go with it.  A journey of a thousand miles continues with the
second step...

JPL Syntax
----------
JPL syntax is trivial, given that you know Java and Perl.  Pretend like
you're writing a native Java method, but say "perl" instead of
"native", and then instead of omitting the body of the method, put your
Perl code in double curlies.  (See Sample.jpl for an example.)

Calling back from Perl to Java is done through the JNI (Java Native
Interface).  No weird transmogrifications are done by the preprocessor
to your Perl code--it's all normal Perl.  The preprocessor just wraps
it up into funny subroutines you don't see unless you peek at the .pl
file it generates.

Installation
------------
There are two ways to install JPL.

The first way gives you the ability to embed Perl in Java programs. You
can also call back into Java from your embedded Perl programs. This should
work well with most JDKs, and is the only option for people using a JDK
that uses green threads (see your JDK documentation). 

The second way lets you embed Java in Perl, but doesn't provide support
for the other direction. This is good, in theory, if you need to work with
a lot of Java classes from within Perl.  I say "in theory," because this 
doesn't actually work a lot of the time.  To use this second way, you
must be using a JDK with native threads.

At this point, the second way is the only way to use JPL under Microsoft 
Windows. Oddly enough, this is the only platform under which the second 
way works!

Installation the First Way (All of JPL)
---------------------------------------
Run "install-jpl".  You have to tell it whether you want to use the
current directory for JPL_HOME or some other directory.  Everything
else should take care of itself, except that after install-jpl
writes the setvars program, you are responsible to invoke it properly
before any JPL applications can be compiled under the current shell.

    sh:   eval `setvars -sh`
    csh:  eval `setvars -csh`
    perl: eval `setvars -perl`;

install-jpl has been tested under:

    Solaris 2.5.1 SPARC, GCC 2.8.0, Perl 5.005_03, JDK 1.1.7
    Debian 2.1 x86, Perl 5.005_60, JDK 1.1.7v3

********************
Solaris 2.5.1 Users:
********************

NOTE: Under Solaris 2.5.1, you may get an error message when install-jpl
builds Sample.jpl:

    You must install a Solaris patch to run this version of the Java 
    runtime.  Please see the README and release notes for more 
    information.
    Exiting.

  This is apparently a spurious message, and it has been reported to 
  Sun.  Although this message aborts the installation, all of JPL is 
  installed by the time this message is reached. To recover and continue, 
  run setvars as described above, cd to the Sample directory, and type
  'make' to continue building. You can then run 'java Sample' to test the 
  example.

  Unfortunately, each time you use 'make' to build a JPL application,
  it will abort when it tries to run 'perl -c' on the generated .pl
  file.  However, you can continue building by typing 'make' again.

Just-JNI (call into Java from Perl only)
----------------------------------------

This has been tested with:

    Debian 2.1 SPARC, Perl 5.005_60, JDK 1.2 beta (crashes with AWT, though)
    Windows NT 4.0 SP4, ActivePerl 519, JDK 1.1.8, Visual C++
    Solaris 7, Perl 5.005_03, JDK 1.1.6, GCC 2.8.1

Solaris 7 Note (this probably applies to all native thread situations):

    Native threads were tricky. I had to build my own Perl, configured with:

    sh Configure -Dprefix=/opt/perl5.005 -Duseshrplib -Doptimize=-g \
                 -Uusemymalloc -D cc=gcc -Dusethreads -d

    When Configure let me edit config.sh, I changed libs to:

    libs='-lthread -lsocket -lnsl -ldl -lm -lposix4 -lpthread -lc -lcrypt'

    The leading -lthread is the only thing I had to add.

How do I do this crazy thing?

1) Cd into the JPL directory. Type the following:

    perl Makefile.PL
    make
    make install

   Under windows, that's:

    perl Makefile.PL
    nmake
    nmake install

3) cd into the JNI directory (cd ../JNI or cd ..\JNI)   

4) We now need to compile and make the Closer.class available to your 
   JPL program.  Closer is a WindowListener that closes the Frame we 
   make in the test program.

   It seems that we've managed to fix the problem with CLASSPATH not
   getting propagated to the JVM, so if '.' is in your CLASSPATH, you
   should be able to compile Closer.java and leave it in the current
   directory:

       javac Closer.java

5) Make the demo:

    a) If you are on Windows, copy typemap.win32:

        copy typemap.win32 typemap

       (this step will probably go away when we clean up some of the
        WIN32 #defines)

    b) type the following:

        perl Makefile.PL
        make
        make test

       Under Windows:

        perl Makefile.PL
        nmake
        nmake test


    c) if all went well, type:

        make install

       or, under Windows:

        nmake install

Mailing List
------------
To subscribe to the jpl mailing list, send an email message to 
jpl-subscribe@perl.org.

CVS Access
----------
Information on accessing the bleeding edge JPL via CVS can be found at:

    http://users.ids.net/~bjepson/jpl/cvs.html

More Info
---------

You can look at the Sample and Test directories, as well as the ../eg
directory for examples.

Perhaps the most important bit of advice we can give you is to watch

    http://perl.oreilly.com

for further information on how to get further information.

Have the appropriate amount of fun.
