On Fri, 2009-06-19 at 09:14 +0300, Abdulaziz Ghuloum 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.),
Oh yeah, I remember the discussion at larceny-users about that [1]. Odd that it worked for Larceny but not PLT. (Implicit phasing needs to win...) > so, maybe you have to do > (import (for (prefix (rnrs) a.) (meta -1))) > in the two auxiliary libraries. I just changed my t2.sps to do that and now PLT does work (i.e. the predicate is broken) and Larceny still works too. > > 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 [...] > > or we can use the previous definition using generate-temporaries. I think the generate-temporaries way should be made to be portable because identifiers which do not come from any lexical context should not have any lexical context. What lexical context could they possibly have which would make any sense? But it does seem hackish because generate-temporaries wasn't intended for this. And likewise, using free-identifier=? seems hackish because we're not actually interested in comparing two identifiers. > But I'm still curious about a portable and pure R6RS solution. Me too. With all these aspects to balance, it's getting challenging :) > 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). That's an interesting conundrum. That's the most interesting example I've seen of this issue. I'm still undecided about this issue. I'll leave it to you experts to compete for the most convincingly better way :) Once I'm convinced, I'm a volunteer mercenary :) [1] http://lists.ccs.neu.edu/pipermail/larceny-users/2009-April/000622.html -- : Derick ----------------------------------------------------------------
