From: Sebastian Tennant <sebyte@smolny.plus.com>
To: guile-user@gnu.org
Subject: Re: Dynamic variable binding
Date: Fri, 19 Dec 2008 11:50:11 +0000 [thread overview]
Message-ID: <r644peoc.fsf@vps203.linuxvps.org> (raw)
In-Reply-To: 200811130051.mAD0pReg006490@fcs13.keithdiane.us
> Quoth Keith Wright <kwright@keithdiane.us>:
>> From: Sebastian Tennant <sebyte@smolny.plus.com>
>>
>> guile> (define-macro (definer var val)
>> `(define ,var ,val))
>> guile> (definer 'foo "bar")
>> guile> foo
>> ERROR: Unbound variable: foo
>> ABORT: (unbound-variable)
>>
>> No doubt this fails for the same reason this does:
>>
>> guile> (define 'foo "bar")
>> guile> foo
>> ERROR: Unbound variable: foo
>> ABORT: (unbound-variable)
>>
>> What exactly happens when you 'define' a symbol?
> I don't know what happens (in Guile), but I can tell
> you what _should_ happen. (In my humble opinion as
> a demi-god of semantics.)
I'm trying to wrap my head around symbols, variables and names of
variables. They seem to me to be three different things.
> (define 'foo "bar")
>
> There are several possibilities
>
> (1) error message in define
> (1a) Rude: Thou fool! |quote| is not a variable
> (1b) Polite: If you are sure you want to do that,
> write out the quote, don't use apostrophe
> (1c) Obscure: Bad variable in def_schkdt
To be really semantically accurate should we not say:
(1a) Thou irrepressible fool! |quote| cannot be the _name_ of a variable.
(1c) Obscure: Bad variable _name_ in def_schkdt.
> But you are asking the wrong question. Ask not
> what happens when a symbol is defined, ask what
> you can do to make the macro define an unquoted
> variable.
Answer: Pass it an unquoted variable.
(define-macro (definer var val)
`(define ,var ,val))
=>
(definer foo "bar")
=>
foo
=> "bar"
:)
Is that the answer you expected?
My semantic point is that the first argument to definer (above) is not a
symbol and it's not a variable (an unbound variable error would be
thrown if it was), so in the context of the first agument to define
there is a third data type; 'variable name'.
Sebastian
next prev parent reply other threads:[~2008-12-19 11:50 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-11-12 19:53 Dynamic variable binding Sebastian Tennant
2008-11-12 22:05 ` Ludovic Courtès
2008-11-13 0:51 ` Keith Wright
2008-12-19 11:50 ` Sebastian Tennant [this message]
2008-12-19 13:03 ` Ludovic Courtès
2008-12-19 15:46 ` Sebastian Tennant
2008-12-20 0:17 ` Keith Wright
2008-12-27 15:56 ` Sebastian Tennant
2008-12-28 22:56 ` Neil Jerram
2008-12-29 10:48 ` Sebastian Tennant
2008-11-13 11:33 ` Sebastian Tennant
2008-11-13 18:50 ` Ludovic Courtès
2008-11-14 6:14 ` Sebastian Tennant
2008-11-15 14:58 ` Jon Wilson
2008-11-15 16:59 ` Sebastian Tennant
-- strict thread matches above, loose matches on Subject: below --
2008-11-12 22:37 dsmich
[not found] <200811130428.mAD4SQbi030880@cm-mail.stanford.edu>
2008-11-13 14:10 ` Kjetil S. Matheussen
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