The L3 language and interface

1 Overview

l3lang(1) is a persistent, interpreted language designed to make interacting with scripts and the data they produce convenient. It does this by keeping track of all computed values (reducing file clutter), providing nested namespaces and functions (avoiding name clashes), and giving point-and-click access to the computed values through the script itself (avoiding the filesystem detour).

It is primarily used through l3gui(1), a worksheet-style interface. Long-running scripts can be executed without the interface, and the results loaded later for interaction.

To avoid the need to learn yet another language, L3 is compatible with a subset of Python and can use any Python library, including Python C/C++ extensions. In particular, the sparx tools (image processing) and NumPy (numerical linear algebra) are known to work. The RPy (statistical computing via R) package also works, but extra care must be taken to make sessions persistent.

In l3gui, every part of a script is an object and its value(s) can be examined via mouse menus, or reinserted into the gui for use in other scripts. This mechanism includes nested loops and function definitions; all values computed in a loop or function can be inspected later.

Scripts and code fragments can be assembled as structures, providing graphical script construction for problems with few steps.

2 Examples

The introduction is somewhat bland, so here are some examples to illustrate why you may want to use L3. They are all included with the gui.

3 Status: developer

The l3 language is functional with some small command-line interface adjustments still needed.

The l3 gui is also usable, but still contains menu entries and cruft more useful for developers than users.

Documentation is very rudimentary and gaps will be filled over the first few months of 2008.

4 Documentation

Manual pages

• l3gui (pdf) — graphical environment for interacting with l3 programs and data.

  The primary l3 interface. Explains the use of the interface, and shows some simple examples.

• l3 (pdf)— interpret l3 programs

  The command-line interface to L3. Used to start long-running jobs in the background or to get an interactive toplevel. Computed results are kept in both cases for later examination.

• l3lang (pdf) — the l3 language.

  The l3 language itself. This is documentation for l3 script writing and tailoring existing Python scripts for direct use inside l3.

5 Installation

The raw files are available from the sourceforge project page, but read the following before installing.

l3lang and l3gui are separate packages, with different prerequisites.

l3lang only requires Python (2.4 or newer) and is therefore trivial to install.

l3gui requires l3lang, Python, pygtk (2.4 or newer), libgnomecanvas, and the canvas part of the gnome-python binding. In recent linux distributions, these are available via the package handling system; follow the system installation steps.

For older or customized systems, use the self-contained alternate installation method.

    cd /tmp
    wget http://downloads.sourceforge.net/l3lang/l3lang-0.3.1.tar.gz
    wget http://downloads.sourceforge.net/l3lang/l3gui-0.3.1.tar.gz
    tar zxf l3lang-0.3.1.tar.gz
    tar zxf l3gui-0.3.1.tar.gz

   man l3
   man l3gui
   l3

   l3gui

    mkdir /your/installer/path
    cd /your/installer/path

    svn co svn://cci.lbl.gov/sparx-installer/trunk \
        sparx-installer

    wget http://cci.lbl.gov/~hohn/sparx-installer.tar.gz
    tar zxvf sparx-installer.tar.gz

    curl http://cci.lbl.gov/~hohn/sparx-installer.tar.gz -o sparx-installer.tar.gz

    cd sparx-installer
    ./configure /your/sparxroot

    cd sparx/l3gui
    make install

6 Licenses

• PLY 1.3.1 – LGPL

  L3 uses version 1.3.1 of PLY, a yacc-like parser generator for Python. Ply is included in the L3 source tree for convenience, but is released under the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.

• L3 – BSD

  L3 itself is released under the following license.

  Copyright (c) 2006, The Regents of the University of California, through Lawrence Berkeley National Laboratory. All rights reserved.

  Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  (1) Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

  (2) Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

  (3) Neither the name of the University of California, Lawrence Berkeley National Laboratory, U.S. Dept. of Energy nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

  You are under no obligation whatsoever to provide any bug fixes, patches, or upgrades to the features, functionality or performance of the source code ("Enhancements") to anyone; however, if you choose to make your Enhancements available either publicly, or directly to Lawrence Berkeley National Laboratory, without imposing a separate written license agreement for such Enhancements, then you hereby grant the following license: a non-exclusive, royalty-free perpetual license to install, use, modify, prepare derivative works, incorporate into other computer software, distribute, and sublicense such enhancements or derivative works thereof, in binary and source code form.

7 Developer download

Development is done using git so anyone can have their own local development branches. The web interface is at repo.or.cz, and you can get the whole repository including l3doc, -lang, and -gui via

git-clone git://repo.or.cz/l3full.git l3full

The working directories can be directly used with appropriate settings, via minimalistic adjustments:

   cd l3full
   export PYTHONPATH=`pwd`:$PYTHONPATH 
   export PATH=`pwd`/l3gui/bin:`pwd`/l3lang/bin:$PATH
   export MANPATH=`pwd`/l3gui/doc/man:`pwd`/l3lang/doc/man:$MANPATH

8 Developer tools

Several parts of l3lang can be used as libraries for other purposes.

tree = reader.parse('''
a = 1
def loop(a):
    if a < 3:
        print a
        loop(a + 1)
loop(1)
''')

print tree.get_infix_string(40)

program:
    a=1
    def loop(a):
        if (a < 3):
            print_(a);loop((a + 1))
    loop(1)

print tree.get_infix_string(10)

program:
    a=1
    def loop(a):
        if (a
        <
        3):
            print_(a)
            loop((a
                +
                1))
    loop(1)

9 Author / Contact info