A quick follow-up. Timothy Sample <samp...@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.... :) -- Tim
