On Jul 23, 2013, at 2:44 PM, Matthew Flatt wrote: > At Tue, 23 Jul 2013 14:24:10 -0400, John Clements wrote: >> Welcome to DrRacket, version 5.3.5.900 [3m]. >> Language: racket; memory limit: 512 MB. >> expanded: '(let-values (((x) '19)) (let-values () x)) >> x-binding: .#<syntax:5:12 x> >> x-use: .#<syntax:8:7 x> >> free-id=? #t >> bound-id=? #t >>> >> >> In particular, this result--that the binding instance of 'x' and the >> macro-introduced use of 'x' are *bound*-identifier=?--surprises me. > > It's because you're looking at a fully expanded form... > >> To take a step back, my low-level understanding > > All correct, as far as I can tell, at the point at which the `getx' > macro has just been expanded. But the next step is to expand/parse `x', > which doesn't just leave the `x' as it was; the `x' expands to an > identifier for the binding of `x'. > > In MtWT, see the 7th rule for `expand', which says > > expand[[id, xi, Sigma]] = <id_new, Sigma> > where (Var id_new) = xi(resolve[[id, Sigma]]) > > The `x' that you have in mind is `id', but the `x' you're checking with > `build-identifier=?' is `id_new'.
Whew! okay, that makes sense. It also explains why xi carries around variable bindings. Now, I just need to think about how that applies to Rust. Many thanks, especially for the swift response. John ____________________ Racket Users list: http://lists.racket-lang.org/users
