4.6 Review - elements of a Forth system
To summarise this chapter:
Forth programs use factoring to break a problem down into small
fragments called words or definitions.
Forth program development is an interactive process.
The main command loop that accepts input, and controls both
interpretation and compilation, is called the text interpreter
(also known as the outer interpreter).
Forth has a very simple syntax, consisting of words and numbers
separated by spaces or carriage-return characters. Any additional syntax
is imposed by parsing words.
Forth uses a stack to pass parameters between words. As a result, it
uses postfix notation.
To use a word that has previously been defined, the text interpreter
searches for the word in the name dictionary.
Words have interpretation semantics and compilation semantics.
The text interpreter uses the value of
state to select between
the use of the interpretation semantics and the compilation
semantics of a word that it encounters.
The relationship between the interpretation semantics and
compilation semantics for a word
depend upon the way in which the word was defined (for example, whether
it is an immediate word).
Forth definitions can be implemented in Forth (called high-level
definitions) or in some other way (usually a lower-level language and
as a result often called low-level definitions, code
definitions or primitives).
Many Forth systems are implemented mainly in Forth.