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Re: What does the coding system nil mean?
From: |
Stefan Monnier |
Subject: |
Re: What does the coding system nil mean? |
Date: |
Mon, 26 Jan 2004 15:07:48 GMT |
User-agent: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.3.50 |
> It's a coding system in the sense that every primitive that accepts a
> coding system symbol also accepts nil.
Try (coding-system-doc-string nil) ;-)
>> Though, I think it's a bit odd for a predicate called
>> `coding-system-p' to return t for an object that is _not_ in fact a
>> coding system.
> IMHO, it's no more odd than this:
> M-: (listp nil) RET => t
Given the fact that the only empty list is nil, I don't find it too odd.
As a former Schemer, I'd agree that it would make sense to introduce a real
empty list constant and stop overloading the meaning of nil, but it's
unlikely to happen.
For coding-systems, you can use `no-conversion' in place of nil, and there
was no historical reason to overload the meaning of nil here.
Stefan