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> So, the two lists ("reserved words", sec. 3.5, and "predeclared
identifiers", sec. 4) are treated
> differently by the compiler:
>
> MODULE PrivNil;
>
> CONST TRUE = 0; NIL = 0;
>
> END PrivNil.
>
> It is allowed to redefine the predeclared identifiers, but not the
reserved words.
Yes, indeed. Reserved words, are treated like punctuation marks in source
code. They are "structuring units" and give the compiler clues about the
layout of the the code. Predeclared identifiers are simple identifiers whose
values are initialized by the compiler.
> Apparently, redefining NIL is far too dangerous -- would break the garbage
collector,
> whereas redefining ENTIER could be useful if the built-in routine has a
bug,
> and redefining INTEGER could be useful when porting ... etc.
>
> Is it correct?
IMHO, there is no compelling reason to make NIL a reserved word or a
predeclared identifier. It's just a design decision for the compiler maker.
It would be interesting to know the opinion of OuS on this point.
Cheers.
Gérard
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Received on Sun Oct 17 2004 - 18:34:16 UTC