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the meaning of #,
- To: AS%hp-labs.csnet@CSNET-RELAY.ARPA
- Subject: the meaning of #,
- From: "David A. Moon" <Moon@SCRC-QUABBIN.ARPA>
- Date: Fri, 13 Jul 84 22:26 EDT
- Cc: COMMON-LISP@SU-AI.ARPA, AS@CSNET-RELAY.ARPA
- In-reply-to: <8407132020.AA10552@HP-VENUS>
Date: 13 Jul 1984 1320-PDT
I am having a lot of trouble understanding the intended meaning of "#," in
compiled code. I find it hard to believe that it is really intended to be
like "#.", as the manual implies. In particular, the result of "#." in a form
becomes PART OF the form. Thus, for example, you can do (DEFMACRO FOO
#.(MUMBLE) ...) and the result of invoking MUMBLE is used as the parameter
list to DEFMACRO. Similarly, if I say (SETQ X #.(MUMBLE)) and MUMBLE returns
a list, then the list will be evaluated. Is the intent that "#," can be used
this way (in compiled code), or can it be used only within quoted structures?
Implementors: How have you implemented "#,"? Are there are restrictions on its
use? If so, can they be stated clearly?
This feature was taken from the Lisp Machine. The intention is that #, can only
be used in constants, not in forms. For example, compiling a file containing
the form (DEFUN FOO () #,BAR) gives an error. (DEFUN FOO () '#,BAR) works.
Anything that the compiler actually has to process at compile time cannot be
a #, since such objects do not exist until load time.
I see what you mean about having a lot of trouble understanding it: the
writeup on #, in the Common Lisp manual is even worse than the writeup
on it in the Lisp Machine Manual.