2018-05-17: Wording changes following the suggestion by JennyBrien
2018-05-29: Specify FIND for words without interpretation semantics, and loosen it for TO IS ACTION-OF. Added Remarks section for a rationale of these additions.
2018-05-23: Initial version
The existing specification of FIND is unclear wrt what xts are returned under what conditions. It also uses a different notion of immediacy from the one in the Definition of Terms. From the rationale of FIND, it is obvious that cmForth inspired the idea that two different xts can be returned. The rationale of COMPILE, shows that the intention is that FIND can be usable for the user-defined text interpreter. But FIND as specified does not guarantee that. This proposal would fix this problem; it is also phrased in a way that includes systems like cmForth and Mark Humphries' system.
Replace the text in the specification of FIND with:
Find the definition named in the counted string at c-addr. If the definition is not found, return c-addr and zero. If the definition is found, return xt 1 or xt -1. The returned values may differ between interpretation and compilation state:
In interpretation state: If the definition has interpretation semantics, FIND returns xt 1 or xt -1, and EXECUTEing xt performs the interpretation semantics of the word. If the definition has no interpretation semantics, FIND may produce c-addr 0; if it produces xt 1 or xt -1, EXECUTEing xt performs a system-dependent action.
In compilation state, the returned values represent the compilation semantics: if xt 1 is returned, then EXECUTEing xt performs the compilation semantics; if xt -1 is returned, then COMPILE,ing xt performs the compilation semantics.
If the definition is for a word for which POSTPONE is ambiguous, it is ambiguous to perform the xt returned by FIND in a STATE different from the STATE during FIND.
In 4.1.2 Ambiguous conditions, add the ambiguous condition above, and remove "6.1.1550 FIND" from
attempting to obtain the execution token, (e.g., with 6.1.0070 ', 6.1.1550 FIND, etc. of a definition with undefined interpretation semantics;
The removal of FIND from the clause in 4.1.2 ensures that we can text-interpret (in compile STATE) words without interpretation semantics, such as IF. The description of the behaviour of FIND for these words in interpretation STATE allows implementations that do not find such words, implementations that return the xt for an error, implementations that return the xt for the compilation semantics, and implementations that return the xt for some system-specific interpretation semantics.
The ambiguous condition allows STATE-smart implementations of TO, IS and ACTION-OF (as Forth-94 and Forth-2012 do).
Note that this does not allow STATE-smart implementations of words without interpretation semantics (e.g., IF), but then, that's already forbidden by POSTPONE and [COMPILE].