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<title>Preface - avram - a virtual machine code interpreter</title>
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<h2 class="unnumbered">Preface</h2>

<p><code>avram</code> is a virtual machine code interpreter.  It reads an input
file containing a user-supplied application expressed in virtual machine
code, and executes it on the host machine. The name is a quasi-acronym
for &ldquo;Applicative ViRtuAl Machine&rdquo;.  Notable features are

   <p><a name="index-functional-programming-1"></a><a name="index-environment-2"></a><a name="index-Unix-3"></a>
     <ul>
<li>strong
support for functional programming operations (e.g., list processing)
<li>interfaces to selected functions from mathematical libraries, such as
          <ul>
<li><code>gsl</code>      (numerical integration, differentiation, and series acceleration)

          <p><a href="http://www.gnu.org/software/gsl/">http://www.gnu.org/software/gsl/</a>
<li><code>mpfr</code>     (arbitrary precision arithmetic)

          <p><a href="http://www.mpfr.org">http://www.mpfr.org</a>
<li><code>minpack</code>  (non-linear optimization)

          <p><a href="http://ftp.netlib.org/minpack">http://ftp.netlib.org/minpack</a>
<li><code>lapack</code>   (linear algebra)

          <p><a href="http://ftp.netlib.org/lapack">http://ftp.netlib.org/lapack</a>
<li><code>fftw</code>     (fast fourier transforms)

          <p><a href="http://www.fftw.org">http://www.fftw.org</a>
<li><code>Rmath</code>    (statistical and transcendental functions)

          <p><a href="http://www.r-project.org">http://www.r-project.org</a>
<li><code>ufsparse</code> (sparse matrices)

          <p><a href="http://www.cise.ufl.edu/research/sparse/SuiteSparse/current/SuiteSparse/">http://www.cise.ufl.edu/research/sparse/SuiteSparse/current/SuiteSparse/</a>
<li><code>glpk</code>     (linear programming by the simplex method)

          <p><a href="http://tech.groups.yahoo.com/group/lp_solve/">http://tech.groups.yahoo.com/group/lp_solve/</a>
<li><code>lpsolve</code>      (mixed integer linear programming)

          <p><a href="http://www.llnl.gov/CASC/sundials/">http://www.llnl.gov/CASC/sundials/</a>
<li><code>kinsol</code>   (constrained non-linear optimization)

          <p><a href="http://www.llnl.gov/CASC/sundials/">http://www.llnl.gov/CASC/sundials/</a>
</ul>
     <li>interoperability of virtual code applications with other console
applications or shells through the <code>expect</code> library
<li>a simple high-level
interface to files, environment variables and command line parameters
<li>support for various styles of stateless or persistent stream
processors (a.k.a. Unix filters)
</ul>

   <p>The reason for writing <code>avram</code> was that I wanted to do some work
using a functional programming language, didn't like any functional
programming languages that already existed, and felt that it would be
less trouble to write a virtual machine emulator than the back end of
a compiler. As of version 0.1.0, the first public release of
<code>avram</code> as such in 2000, most of the code base had been in heavy
use by me for about four years, running very reliably. At this writing
some six years later, it has seen even more use with rarely any
reliability issues, in some cases attacking large combinatorial
problems for weeks or months at a time. These problems have involved
both long running continuous execution, and batches of thousands of
shorter jobs.

   <p>Although the virtual machine is biased toward functional programming,
it is officially language agnostic, so <code>avram</code> may be useful to
anyone involved in the development of compilers for other programming,
scripting, or special purpose languages. The crucial advantage of
using it in your own project is that rather than troubling over
address modes, register allocation, and other hassles inherent in
generating native code, your compiler can just dump a fairly high
level intermediate code representation of the source text to a file,
and let the virtual machine emulator deal with the details. The
tradeoff for using a presumably higher level interpreted language is that the
performance is unlikely to be competitive with native code, but this
issue is mitigated in the case of numerical applications whose heavy
lifting is done by the external libraries mentioned above.

   <p>Portability is an added bonus. The virtual code is binary compatible
across all platforms. Versions of <code>avram</code> as of 0.1.0 and later are
packaged using GNU autotools and should be possible to build on any
platform supporting them. In particular, the package is known to have
built successfully on MacOS, FreeBSD, Solaris (thanks to the compile
farm at Sourceforge.net) Digital Unix, and Debian GNU/Linux for i386 and
Alpha platforms, although it has not been extensively tested on all of
them. Earlier versions were compiled and run successfully on Irix and
even Windows-NT (with <samp><span class="command">gcc</span></samp>).

   <p>This document is divided into three main parts, with possibly three
different audiences, but they all depend on a basic familiarity with
<a name="index-Unix-4"></a>Unix or GNU/Linux systems.

     <dl>
<dt><a href="User-Manual.html#User-Manual">User Manual</a><dd>essentially reproduces the information found in
the manpage that is distributed with <code>avram</code> with a few extra
examples and longer explanations. Properly deployed,
<code>avram</code> should be almost entirely hidden from end users by wrapper
scripts, so the &ldquo;users&rdquo; to whom this part is relevant would be
those involved in preparing these scripts (a matter of choosing the right
command line options). Depending on the extent to which this task is
automated by a compiler, that may include the compiler writer or the
developers of applications. 
<br><dt><a href="Virtual-Machine-Specification.html#Virtual-Machine-Specification">Virtual Machine Specification</a><dd>documents much of what one would need to know in order to write a
compiler that generates code executable by <code>avram</code>. That includes
the complete virtual machine code semantics and file formats. It would
also be possible to implement a compatible replacement for <code>avram</code>
from scratch based on the information in this chapter, in case anyone
has anything against C, my coding style, or the GPL.  (A few patches to
make it <samp><span class="command">lint</span></samp> cleanly or a new implementation in good
pedagogical Java without pointers would both be instructive
exercises. ;-))
<a name="index-pointers-5"></a><a name="index-Java-6"></a><br><dt><a href="Library-Reference.html#Library-Reference">Library Reference</a><dd>includes documentation on the application program interface and
recommended entry points for the C library distributed with
<code>avram</code>. This information would be of use to those wishing to
develop applications incorporating similar features, or to reuse the
code for unrelated purposes. It might also be useful to anyone wishing
to develop C or C++ applications that read or write data files in the
format used by <code>avram</code>. 
</dl>

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