FAST Forth Native-Language Embedded Computers

A Forum for Exploring Forth Issues and Promoting Forth
Forth: Always New, Despite its Age
Whenever we send out a Forth marketing message, we
need to speak of Forth using the latest terminology on the
high-tech horizon. Two terms to consider with regard to
Forth are "application framework" and "introspection."
Did you know that, among other things, Forth is a
deuelopment system framework and a programming lan-
guage framework?As the term framework implies, it frames
your program with a structure to carry the code you supply.
A framework offers another form of code reuse. The
most familiar format for reusable code is a library, which
consists of bundled service-providing routines that you
choose to call or not. Besides offering already-made
services, the framework "prewires" certain services to-
gether to roughly model the application you are about to
build. The framework offers a basic design for accomplish-
ing a task, instead of offering piecemeal code that you may
use along with your own design.
Frameworks such as Hypercard and MacApp are help-
ing application programmers create GUI applications for
The actual processor is
less of a concern than
the virtual processor...
the Macintosh with greatly reduced effort. For PCs running
Windows, the premier framework is Visual BASIC.
The code from the framework satisfies general goals,
such as queuing the input events associated with a mouse
and keyboard. ~~~lication-specific goals are met by your
own routines, which the framework has a way to call at the
appropriate times.
Forth can be seen not merely as an application framework
(particularly if your final application preserves the
Forth interpreter), but also as a development system
framework and a programming language framework.
The Forth programming language is subject to modification
by the programmer. Typically, control structures
are written to replace the ones that came with a system.
Because it does not involve redesigning Forth from the
ground up, this type of language refinement is equivalent
to the use of a framework. In this way, Forth functions as
a programming language framework. (The end product is
a Forth dialect or a new language-typically one that
preserves the basic Forth compiler.)
Habitually, Forth programmers create decompilers,
tracers, code profilers, and other tools. In Forth, they are
easy to create. In this case, Forth is functioning as a
development system framework-allowing you to create
specific development tools within an overall tool frame-
work. (The end product is a customized application
development system that preserves most of Forth's native
development tools.)
The term framework helps convey an important mes-
sage to the larger programming community. It is one way
that Forth can be considered a very progressive, and a very
high-level, environment.
Programs Become Introspective
Another new term we can use to describe Forth involves
the concept of introspection. This term came to my attention
recently with regard to Dylan. The Dylan programming
language is a product of long-term research at Apple
Computer. Dylan is object oriented, so the concept of
introspection is the concept of self-identifying objects:
The [Dylan] language should contain features for
introspection. This means that the language run-time
should have sufficient power to answer questions about
itself and the objects it manages. For example, it should
be possible at execution time to analyze the structure of
an object, find the subclasses of a class, etc.
To facilitate type-safety and introspection, objects are self-
identifjring in memory. Unless all uses of an object can be
analyzed at compile-time, the run-time memory for the
object should contain enough information to identify its
class and value. --&Ian Language Reference
The ease with which Forth decompilers can be written
suggests that Forth compilers already produce memory
images that are subject to meaningful inspection.
Several Forth programmers at the Asilomar FORML
conference last year were interested in developing Forth
March 1994 April 42 Forth Dimensions