Review - elements of a Forth system (Gforth Manual)

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 depends 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.