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5.1 Notation

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.

Stack effect

The stack effect is written in the notation before -- 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 the types.

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 Forth standard is divided into several word sets. A standard system need not support all of them. Therefore, in theory, the fewer word sets your program uses the more portable it will be. However, we suspect that most Standard Forth systems on personal machines will feature all word sets. Words that are not defined in Standard Forth have gforth or gforth-internal as word set. gforth describes words that will work in future releases of Gforth; gforth-internal words are more volatile. Environmental query strings are also displayed like words; you can recognize them by the environment in the word set field.


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. false or true.




Cell, can contain an integer or an address


signed integer


unsigned integer


double sized signed integer


double sized unsigned integer


Float (on the FP stack)


Cell-aligned address


Char-aligned address (note that a Char may have two bytes in Windows NT)


Float-aligned address


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

ior, wior

I/O result code, cell-sized. In Gforth, you can throw iors.


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 <> quotes.

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