It is pretty common for applications to offer extension capabilities
by means of a simple "extension language". Usually this language is
invented for the particular application, rather than simply picking
one of the many available interpreters. This forces users to learn
a new language just to be able to use the program.
In contrast, early versions of Siag used Scheme as its interpreter.
The implementation chosen was SIOD by George Carrette. This concept
has now been taken even further by adding support for multiple
The supporting code for each language resides in its own module.
As an example, Siag can currently be linked with support for these
Pathetic Writer and Egon Animator can be linked with SIOD, Guile, Ruby
- The default syntax for expressions in Siag is a simple C-like
syntax, familiar to anyone who has used a spreadsheet before.
- An extremely small Scheme interpreter which cooperates
exceptionally well with C.
- Optional; another Scheme interpreter. This one follows the R4RS more closely
than SIOD, which can be important if external Scheme programs are to
be used in Siag.
- Optional. Tcl is another popular embeddable scripting language.
One interpreter can call another using a string-based interface.
In SIOD, a call to make Tcl beep can look like this:
(exec-expr 'Tcl "puts \\a")
And Tcl can tell Guile to collect garbage in the following fashion:
exec-expr Guile "(gc)"
Getting the optional interpreters to work can be a bit tricky. The
INSTALL document includes several hints that are likely to be of
Ulric Eriksson - January 2002 - email@example.com