(followups trimmed to dev; is that an acceptable strategy?) On Nov 24, 2010, at 12:44 PM, Robby Findler wrote:
> On Wed, Nov 24, 2010 at 1:49 PM, John Clements > <cleme...@brinckerhoff.org> wrote: >>> On Wed, Nov 24, 2010 at 11:05 AM, Robby Findler >>> <ro...@eecs.northwestern.edu> wrote: >>>> On Wed, Nov 24, 2010 at 12:55 PM, Joe Marshall <jmarsh...@alum.mit.edu> >>>> wrote: >>>>>> On Nov 20, 2010, at 6:58 PM, Matthias Felleisen wrote: >>>>>> >>>>>>> Hygiene is a technical term. The idea is roughly that >>>>>>> the __macro system__ (as a whole) should respect the >>>>>>> lexical structure of your program. >>>>> >>>>> It is somewhat unfortunate that the name `hygiene' has caught >>>>> on here. It really ought to be called `lexical scoping' (with the >>>>> understanding that macros have no special permission to violate >>>>> lexical scope any more than lambda bindings do). >>>> >>>> You know about Oleg's macro called, bind-x-to-5 that has one >>>> subexpression does exactly its name claims, but in a hygenic macro >>>> system? >> >> Hang on... you're still using the term "hygienic" in the non-Felleisen way. > > No I'm not. > >> That is, if we accept that a hygienic system is one that has well-defined >> behavior but where you can bind new names when you explicitly ask to, then >> >> #lang racket >> >> (define-syntax (bind-x-to-5 stx) >> (syntax-case stx () >> [(_ exp) >> #`(let ([#,(datum->syntax stx 'x) 5]) >> exp)])) >> >> (bind-x-to-5 x) >> >> ...is a legal macro in a hygienic macro system. > > Sure. > > But Oleg's macro doesn't do that. Right, I understand. Oleg shows that you can bind x even in a macro system that doesn't allow variable capture in the way that I used here; in other words, variable capture is possible even in a system-without-XXX, where XXX refers to the property of being able to do what I did here (straightforward variable capture). IIUC, you use the word "hygienic" in the paragraph above (when you say "but in a hygienic macro system") to mean "system-without-XXX", but Matthias' point is that hygienic *doesn't* mean "system-without-XXX", it just means "system-where-XXX-can-only-occur-deliberately." Naturally, this conversation would be simpler if we had a word for XXX... :) John
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