Hi Thorsten,

> I wonder if one could build a picolisp app that fully integrates with R
> (statistics software, http://www.r-project.org/) and GRASS GIS (a command
> line GIS that uses a superset of shell commands, http://grass.fbk.eu/) on
> its linux host machine?

There are basically five ways a PicoLisp program can be integrated with
other software:

1. Call existing library functions

   This is available only in the 64-bit version with the 'native'
   function. C functions can be directly called from Lisp code. For an
   extensive example, look at "lib/openGl.l".

2. Write a shared object file (DLL)

   This is analog in the 32-bit and 64-bit versions, but due to the
   underlying implementation such shared object files are written in C
   for the 32-bit version, and in assembly for the 64-bit version.
   Examples are the 'ext' and 'ht' libraries, built in the Makefile's
   ("src/ext.c", "src/ht.c", "src64/ext.l" and "src64/ht.l").

3. Write inline C code

   The 32-bit and 64-bit versions of PicoLisp behave a little different
   here. In the 32-bit version, these functions must contain glue code
   to convert between C and Lisp data. The file "misc/crc.l" contains an
   example for both versions.

4. Start other programs as sub-processes, and communicate with their
   standard I/O via pipes. This can be done with the 'in', 'out' and
   'pipe' functions.

5. Use sockets or some other type of IPC (e.g. named pipes) to
   communicate with another program.

Did I forget some other way?

> It's always claimed that clojure is great because it has access to countless
> java libraries on the jvm. But clojure is all about functional programming,

BTW, there is also ErsatzLisp, a subset of PicoLisp written in Java. It
provides for some ways to call the underlying JVM.

> concurrency and avoiding mutable state, while java is all about objects with
> mutable state. So it would only make sense for a clojure program to call
> java libraries like pure functions without side effects and use the return
> value, otherwise the clojure clean and scalable programming model would be
> messed up.

Yep. The same problems apply to ErsatzLisp.

> Can't picolisp do this too? Call Java (and C, C++, Python ...) functions

Several years ago, the PicoLisp GUI depended heavily on Java applets.
This stuff is still available as a separate tarball "picoJavaGUI.tgz".
It also contains a file "lib/java.l" which provides an interface to a
separately running JVM. This was never really used, though.

In one project we communicated with C++ programs via a PLIO library.
PLIO is the format used by PicoLisp internally for marshalling database
objects, for the 'pr' and 'rd' functions, and family IPC ('tell' etc.).
A skeleton for PLIO can be fetched from "software-lab.de/plio.tgz".

I'll gladly explain more details if you have specific questions :)

- Alex
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