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TG9541 / stm8ef

STM8 eForth - a user friendly Forth for simple µCs with docs
https://github.com/TG9541/stm8ef/wiki
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Replace COMPILE and [COMPILE] with POSTPONE? #413

Closed TG9541 closed 3 years ago

TG9541 commented 3 years ago

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.

TG9541 commented 3 years ago

This is now getting more serious ;-)

TG9541 commented 3 years ago

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 commented 3 years ago

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).