It looks as though some initial write-up was deleted.
Forth is a programming language that was created in 1970
by Charles Moore. One of the things that make it interesting is that Forth combines the functions of operating system and programming
language. It is a stack-based language: most, if not all,
commands manipulate the stacks in some way. Forth uses
two stacks: a data stack and a return stack. It is also
possible to temporarily store data on the return stack.
Because it is stack based, Forth's commands are postfix (Reverse Polish Notation). For example,
(a + b) / c
would be written in Forth as
a b + c /
One of the points of writing commands in this way
is that it is optimized for the computer: this is
how the computer would do it anyway: it pushes the
operands onto the stack and then executes the
function.
It might seem that a language that consists
of such primitive functions would be difficult
to work with. On the contrary, development time
in Forth is very fast and relatively bug-free,
as compared with other languages. The reason
being, that it is easy to declare "words" in
Forth that encapsulate functionality. To put it
another way, Forth programmers create a new
language each time they write a program.
(Scheme and Lisp enthusiasts should recognize
this rationale.)
Forth is still very much alive and is found, for
example, on every Sun microcomputer in the Open
Boot PROM.