> (define (bound-identifier? id) (and (id->label id) #t)) Why the (and <> #t) wrapper?
On Fri, Jun 19, 2009 at 4:14 PM, Abdulaziz Ghuloum<aghul...@gmail.com> wrote: > > On Jun 19, 2009, at 2:27 AM, Derick Eddington wrote: > >> On Thu, 2009-06-18 at 22:55 +0300, Abdulaziz Ghuloum wrote: >>> >>> (define (unbound-identifier? x) >>> (and >>> (free-identifier=? x (datum->syntax a.ctxt (syntax->datum x))) >>> (free-identifier=? x (datum->syntax b.ctxt (syntax->datum x)))))) >> >> That's clever, but it's broken: > > oops. > >> It seems PLT and Ypsilon are broken about this because an unbound a.cons >> and a bound a.cons must not be free-identifier=?. > > Actually, I didn't expect that definition to work at all for PLT and > Larceny since their notion of free-identifier=? is very different from > Ikarus's (w.r.t. phases of identifiers: whether a bound identifier in > level x is free-identifier=? to the same identifier bound in level y, > etc.), so, maybe you have to do > (import (for (prefix (rnrs) a.) (meta -1))) > in the two auxiliary libraries. > > For ypsilon, there are definitely bugs: in t.ss, you see that "let" > is bound, while if you test for "cons", you find it unbound. > >> I'm thinking there should be a standard (or common and portable with >> compat libraries) primitive identifier-bound? predicate. > > We first need to establish if it can be implemented in pure R6RS or > not. In psyntax, it can be implemented as easily as: > > (define (bound-identifier? id) (and (id->label id) #t)) > > or we can use the previous definition using generate-temporaries. > But I'm still curious about a portable and pure R6RS solution. > > BTW, in Larceny, you cannot do something like > > (when-unbound (x) > (define x ---)) > > It complains that "Definition of identifier that may have already > affected meaning of undeferred portions of body". This is allowed > by the report (with a "should" iirc). > > Aziz,,, >
