From: the.beez.speaks@gmail.com
On 19-09-2024 10:36, albert@spenarnc.xs4all.nl wrote:
> In article ,
> Hans Bezemer wrote:
>> On 18-09-2024 12:34, Ruvim wrote:
>>> Actually, most Forth systems are classic single-xt systems. And most
>>> educational materials on how to implement Forth explain the classic
>>> single-xt approach.
>>
>> Interesting enough - considering this "dual xt" idea, 4tH has *ALWAYS*
>> been "dual xt". All compilation behavior is in the compiler and all
>> execution behavior is in the interpreter. Note 4tH *only* contains
>> primitives. The Forth layer is what you build with these primitives,
>> since both the compilation behavior and execution behavior is coded in C.
>
> And the opposite approach. Always have default compilation semantics,
> i.e. add the behaviour of an interpreted word to a compiled word.
That is handled by two tables in the 4tH compiler: one to add primitive
words *WITH* an argument (like built-in constants) and one for words
*WITHOUT* (like DUP, ROT, PARSE, etc).
Words which do not translate to simple "instruction(argument)" pairs are
in the third table (IF, VALUE, :, ;, etc.) And then there's the symbol
table which again, contains simple "instruction(argument)" pairs.
> If the compilation stack is separate, inspection of STATE
> can be restricted to INTERPRET , without even a need to
> be inspected by number, aka denotations.
> INTERPRET could simply inspect if the stack has changed.
> In compile mode, it compiles literals, instead of leaving
> them on the stack.
In certain situations the growing compilant is used as a stack in 4tH
i.e. the last word compiled *MUST* be a LITERAL for it to work.
Fortunately, the 4tH optimizer does a great job when constant folding.
Hans Bezemer
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