[racket-dev] A curious question about quote

Like Joe said.  I think that this "quote" behavior is a very practical 
convenience that Scheme inherited, not something about which to hurt 
one's brain trying to discern the underlying pure truths.

There are some confusing bits.  For example:

#lang racket
(equal? (quote 1) 1) ;==> #t
(equal? (quote (quote 1)) (quote 1)) ;==> #f

This particular confusion, we can clarify or rationalize as "(quote 
<NUMBER-LITERAL>)" being a very different thing than "(quote 
<LIST-LITERAL>)".  Which, as you said, could be seen as conflating.

Taking another look at the above quirk suggests "quote" having 
simple-minded automagic to decide which of its multiple personalities 
(number or list) is triggered:

(quote 1) ;==> 1
(quote (quote 1)) ;==> (quote (quote 1))

I don't know/recall how CL philosophizes about this.  Emacs Lisp people 
talked about syntax like numeric literals, "nil", and "t" being 
``self-quoting.''  Scheme people tend talk about numeric literals being 
``self-evaluating,'' but I don't see how that explains the quirk above.

If you can work out a clean formalism for the syntax/reader that avoids 
quirks like these, yet still provides the list construction convenience 
that permits non-list constants/self-evals elements without extra syntax 
for quoting or unquoting them, I think that would be good.

As long as you're banging around in there, if you can also replace the 
names "unquote" and "unquote-splicing" (which I believe are hardly ever 
used literally in application code) with names/syntax that don't stomp 
on the space of names application code might want to use in, say, quoted 
or quasiquoteed embedded SXML, that would be even better.  :)  I wish 
that RnRS had gotten rid of these at the same time that it blessedly got 
rid of "nil" and "t".  What currently makes more sense to me in Racket 
is to move to "#unquote" and "#unquote-splicing" (or "#," and "#,@"), 
keeping the same "," and ",@" shorthand.  I suspect that changing to 
those would be backward-compatible for 99.9% existing code outside of 
Racket internals.  I could be overlooking some case that makes that 
change a bad idea, of course.

Joe Marshall wrote at 01/26/2011 05:17 PM:
> On Wed, Jan 26, 2011 at 8:02 AM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:
>   
>> I have a historical question about quoted constants. Does anyone know why '1 = 1? My intuition is that this is an artifact of conflating quote with list constructors. Is that indeed the case?
>>     
>
> I doubt it.  More likely it was when someone realized that if (quote 1) is not the number 1, then everyone would be confused.  What else would it be?
>   

-- 
http://www.neilvandyke.org/
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