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From: Tim Bradshaw <t...@tfeb.org>
Newsgroups: comp.lang.lisp
Subject: Re: characters in CL
Date: Fri, 18 Mar 2011 09:55:07 +0000
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On 2011-03-18 08:19:32 +0000, Mark Tarver said:

> 
> You can think of them as having strings composed of substrings, with
> a
> fixed composition mechanism.

I think that this kind of thing is basically a disaster for a language 
which wants to have a coherent type system.  You really, I think, have 
two options:

	strings are a special magic type orthogonal to any other type (in
	particular they are not arrays or sequences);

	strings are some kind of sequence/array type.

For a language which is not entirely about string bashing the latter 
option is the obvious one.  Then you have to ask the question: what 
type are strings sequencs of?  The answer can't be "strings" because 
then the type system falls to bits in some horrible way: you need 
another type (or the option of another type: strings could be sequences 
whose elements are (strings OR <something>).)  That other type, in CL, 
is characters.

The other option, having strings *not* be sequences but some special 
magic type is possible, and I suspect it's basically what Perl does, 
for instance (in so far as Perl has a coherent type system at all).  I 
would not want CL to do this.

I don't know how this maps on to unicode: I do know that unicode has 
lots of cases where complicated things happen, and I also know that I 
don't understand it.  Unfortunately the only person I knew who I was 
sure really *did* understand it is dead, so we can't get his opinion.  
I don't think that the sharp-s / ss thing in German has much to do with 
this, because there are lots of complicated rules around that (which I 
can no longer remember). It may be that assuming things like 
string-upcase / char-upcase &c are simple is just a huge mistake.

--tim