The difference of this chapter from the Tutorial (see Forth Tutorial) is that it is slower-paced in its examples, but uses them to dive deep into explaining Forth internals (not covered by the Tutorial). Apart from that, this chapter covers far less material. It is suitable for reading without using a computer.
The primary purpose of this manual is to document Gforth. However, since Forth is not a widely-known language and there is a lack of up-to-date teaching material, it seems worthwhile to provide some introductory material. For other sources of Forth-related information, see Other Forth-related information.
The examples in this section should work on any Standard Forth; the
output shown was produced using Gforth. Each example attempts to
reproduce the exact output that Gforth produces. If you try out the
examples (and you should), what you should type is shown like this
and Gforth’s response is shown like this. The single exception is
that, where the example shows RET it means that you should
press the “carriage return” key. Unfortunately, some output formats for
this manual cannot show the difference between this and
this which will make trying out the examples harder (but not
impossible).
Forth is an unusual language. It provides an interactive development environment which includes both an interpreter and compiler. Forth programming style encourages you to break a problem down into many small fragments (factoring), and then to develop and test each fragment interactively. Forth advocates assert that breaking the edit-compile-test cycle used by conventional programming languages can lead to great productivity improvements.