[racket] Plea for neologism (was: Re: letoverlambda)

From: Robby Findler (robby at eecs.northwestern.edu)
Date: Wed Nov 24 14:38:21 EST 2010

On Wed, Nov 24, 2010 at 1:23 PM, Joe Marshall <jmarshall at alum.mit.edu> wrote:
> On Wed, Nov 24, 2010 at 11:05 AM, Robby Findler
> <robby at eecs.northwestern.edu> wrote:
>> On Wed, Nov 24, 2010 at 12:55 PM, Joe Marshall <jmarshall at 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?
> Yes.  And I have to admit that I've used this trick myself to write
> some questionable (but useful) macros.
>> That example suggests to me that what is called hygiene should
>> probably not be called lexical scope.
> I'm not sure.  Certainly the r5rs hygienic macro system has the
> ability to mimic non hygienic use.
> But consider these statements:
>  `Any sufficiently powerful macro system can appear to break
>   lexical scope.'
>  `Any macro system weak enough to preserve lexical scope is
>   too weak to do X'  (where X is something one would normally
>   expect to be able to do with a macro)
> I have not seen a claim or proof of either of these or a denial
> of either.  In other words, perhaps there is a macro system that
> is both sufficiently powerful and general that we'd all agree it
> qualifies as a macro system, yet is weak enough that we all agree
> it cannot violate what we consider `lexical scope'.

I consider Oleg's example (which doesn't use datum->syntax or anything
fancy like that) to be an example to substantiate the first sentence

> Alternatively, perhaps one could argue that our understanding of
> `lexical scope' is too narrow and primitive, and that Oleg's
> bind-x-to-5 macro is simply a surprising, but consequential artifact
> of the true meaning of `lexical scope'.

That might be true but I don't like it either.

> I rather prefer the former alternative.  The current macro system is
> an amazing piece of insight and engineering, but it does have a few
> dark corners:  Oleg's bind-x-to-5 is one, accidental export of internal
> bindings is another.

IMO, the macro system is good, but the phrase "lexical scope" is bad
and we should find another one that is more accurate and helps get at
the essence of why we consider the macro system good.

Dave Herman may have an opinion here. :)


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