[IMMEDIATE] for Standard Forth

Eric Blake eblake@redhat.com

Version 0.9.0 - 2025-08-10

This package provides an implementation of [IMMEDIATE] on top of ANS Forth-2012. It is provided in the public domain.

Example

Declare RDROP as an immediate word.

: RDROP [IMMEDIATE] ( R: x -- )
  POSTPONE R> POSTPONE DROP ;

Background

[IMMEDIATE] solves an ambiguity present in the use of IMMEDIATE. In standard Forth, IMMEDIATE is generally non-immediate, and it is ambiguous if you attempt to use it while a current definition is underway (for example, ": foo ; : bar [ IMMEDIATE ] ;" differs between implementations on whether foo or bar is made immediate). However, some other Forth variants (including JonesForth) have provided IMMEDIATE as an immediate, and used the style ": name IMMEDIATE body... ;", on the grounds that you want to declare intent as soon as possible, where having to scroll to learn whether a word is immediate goes against that design principle.

This package works around the ambiguity of IMMEDIATE by adding the word [IMMEDIATE] which may be safely used within the body of : ;. If your Forth supports :NONAME, then [IMMEDIATE] is explicitly a no-op in the body of :NONAME ;, in order to make it easier to copy-and-paste definitions without regards to whether the definition will be named or anonymous. This package also makes it easy to declare a meta-programming word ": imm: : POSTPONE [IMMEDIATE]" (although that word is not provided here).

Tests

The following tests, in the syntax of John Hayes test framework tester.fs, show expected results.

t{ : is-immediate ( "name" -- flag ) BL WORD FIND NIP 1 = ; -> }t
t{ : foo [IMMEDIATE] ; -> }t
t{ : bar ; -> }t
t{ :NONAME [IMMEDIATE] ; EXECUTE -> }t
t{ is-immediate foo -> -1 }t
t{ is-immediate bar -> 0 }t
t{ : baz ; [IMMEDIATE] -> }t
t{ is-immediate baz -> -1 }t
t{ : imm: ( "name" -- colon-sys ) : POSTPONE [IMMEDIATE] ; -> }t
t{ imm: my-imm ; -> }t
t{ is-immediate my-imm -> -1 }t

Tests have been run successfully on

• gforth, 0.7.3 and 0.7.9
• SwiftForth, 3.12.0

Bug Reports

Please send bug reports, improvements and suggestions to Eric Blake <eblake@redhat.com>. See also this ForthHub post.

Conformance

This program conforms to Forth-2012

Standard conformant labeling

This is an ANS Forth Program,

- Requiring the Core word set.
- Requiring `\ TRUE` from the Core Extensions word set.
- Requiring `[DEFINED] [IF] [THEN] [UNDEFINED]` from the
  Programming-Tools Extensions word set.
- Redefining `:NONAME` from the Core Extensions word set if
  available.

- After loading this program, a Standard System still exists.