The Forth words are described in this section in the glossary notation that has become a de-facto standard for Forth texts:
word Stack effect wordset pronunciation
The name of the word.
The stack effect is written in the notation
after, where before and after describe the top of
stack entries before and after the execution of the word. The rest of
the stack is not touched by the word. The top of stack is rightmost,
i.e., a stack sequence is written as it is typed in. Note that Gforth
uses a separate floating point stack, but a unified stack
notation. Also, return stack effects are not shown in stack
effect, but in Description. The name of a stack item describes
the type and/or the function of the item. See below for a discussion of
All words have two stack effects: A compile-time stack effect and a run-time stack effect. The compile-time stack-effect of most words is – . If the compile-time stack-effect of a word deviates from this standard behaviour, or the word does other unusual things at compile time, both stack effects are shown; otherwise only the run-time stack effect is shown.
Also note that in code templates or examples there can be comments in
parentheses that display the stack picture at this point; there is no
-- in these places, because there is no before-after situation.
How the word is pronounced.
The wordset specifies whether a word has been standardized, it is an
environmental query string, or if it is a Gforth-specific word. In
the latter case the wordset contains the string
wordset names are either
environment of refer to standard word
The Forth standard is divided into several word sets. In theory, a standard system need not support all of them, but in practice, serious systems on non-tiny machines support almost all standardized words (some systems require explicit loading of some word sets, however), so it does not increase portability in practice to be parsimonious in using word sets.
For the Gforth-specific words, we have the following categories:
We intend to permanently support this word in Gforth and it has been available since Gforth <version> (possibly not as supported word at that time).
This word is available in the present version and may turn into a permanent word or may be removed in a future release of Gforth. Feedback welcome.
This word is an internal factor, not a supported word, and it may be removed in a future release of Gforth.
This word will be removed in a future release of Gforth.
A description of the behaviour of the word.
The type of a stack item is specified by the character(s) the name starts with:
Boolean flags, i.e.
Cell, can contain an integer or an address
double sized signed integer
double sized unsigned integer
Float (on the FP stack)
Char-aligned address (note that a Char may have two bytes in Windows NT)
Address aligned for IEEE double precision float
Address aligned for IEEE single precision float
Execution token, same size as Cell
Word list ID, same size as Cell
I/O result code, cell-sized. In Gforth, you can
Pointer to a name structure
string in the input stream (not on the stack). The terminating character
is a blank by default. If it is not a blank, it is shown in