Re: Inconsistencies with free-identifier=? and bound-identifier=?

[Jean Abou Samra <jean@abou-samra.fr>]

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Le jeudi 27 juillet 2023 à 16:10 -0600, Timothy Sample a écrit :
> A quick follow-up.
> 
> Timothy Sample <samplet@ngyro.com> writes:
> 
> > Lastly, you should read section 3.1 of “Binding as Sets of Scopes”:
> > 
> >    
> > https://www-old.cs.utah.edu/plt/scope-sets/general-macros.html#%28part._.Identifier_.Comparisons_with_.Scope_.Sets%29
> > 
> > It shows that ‘bound-identifier=?’ gives false negatives in both
> > sets-of-scopes and marks-and-substitutions hygiene systems.  (I didn’t
> > 
> > test that example or anything, but I thought it fit the theme of
> > identifier predicate arcana pretty well.)
> 
> Actually, read section 3.2.  It covers your example exactly.  Discussing
> the example
> 
> > (free-identifier=? (let ([x 1]) #'x)
> >                    #'x)
> 
> it says,
> 
> > Note: Racket’s macro system matches Dybvig et al. (1993), where both
> > free-identifier=? and bound-identifier=? produce #f for the above
> > arguments, and bound-identifier=? always implies
> > free-identifier=?. The current psyntax implementation, as used by Chez
> > Scheme and other implementations and as consistent with Adams (2015),
> > produces #f and #t for free-identifier=? and bound-identifier=?,
> > respectively; as the example illustrates, bound-identifier=? does not
> > imply free-identifier=?. The set-of-scopes system produces #t and #t
> > for free-identifier=? and bound-identifier=?, respectively, and
> > bound-identifier=? always implies free-identifier=?.
> 
> You can actually control what ‘free-identifier=?’ returns for the above
> example using “scope pruning” when quoting syntax.  Those Racketeers
> really have their act together....  :)


Oh, wow! I definitely need to read that paper. Thank you very much.

Cheers,
Jean




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