Replace COMPILE and [COMPILE] with POSTPONE?

[TG9541]

More modern Forth implementations than eForth have long replaced COMPILE and [COMPILE] with the more general word POSTPONE.

The difference between the old and the new approach is this:

1. Compile a regular word:
   a: : test1a COMPILE DROP ; => <CALL XT-COMPILE><CALL XT-DROP>
   b: : test1b POSTPONE DROP ; => <LIT XT-DROP><CALL XT-CALL,>

2. Compile an IMMEDIATE word:
   a: : test2a [COMPILE] IF ; => <CALL XT-IF>
   b: : test2b POSTPONE IF ; => <CALL XT-IF>

When used as "macros" or directly as IMMEDIATE the words test1a - test2a and test1b - test2b perform the same thing (COMPILE in test1b has to work around any STM8 eForth code optimization features which can be a big issue)

There is an edge case when [COMPILE] is used to compile a regular word:
a: : test3a [COMPILE] DROP ; => <CALL XT-DROP>
b: : test3b POSTPONE DROP ; => <LIT XT-DROP><CALL XT-CALL,>

Other edge cases exist if any of the words POSTPONE, COMPILE or [COMPILE] is used with words defined by CREATE, CONSTANT or VARIABLE. I'll have to check what the "the standard` has to say about that.

Before doing any such change I'd like to get some input from the community.

• is ALIASing the legacy words to POSTPONE an acceptable solution?
• would you expect the original words to be retained, and if yes, why so?

[TG9541]

This is now getting more serious ;-)

[TG9541]

I've found a problem in >REL, the relative addressing compiler overlay for IF ... ELSE ... THEN:

I hadn't realized that ] isn't flagged IMMEDIATE (it doesn't need to be since it starts the compiler) and had compiled it with [COMPILE]. This has no effect whatsoever unless that's an alias for POSTPONE. The problem is easy to fix ( -> #419 ) but [COMPILE] masks such errors and one has to be careful when replacing that word.

[TG9541]

Using POSTPONE in the lib worked fine. I'll now turn off the legacy words in defconf.inc. If some code needs them they can be selected in a downstream build configuration (e.g. in globconf.inc).

By default the aliases COMPILE and [COMPILE] are in the target folder. Just take care not to use the [COMPILE] alias on a non-IMMEDIATE word (which is now from now on "officially" an error).