Re: [PATCH] Add new lisp function length= with bytecode support

[Paul Eggert]

On 02/27/2017 10:43 AM, Gdobbins wrote:
> I looked in the manual for a place where length= should be documented, 
> but didn't find one. I thought the docstring was sufficient. Perhaps I 
> was mistaken.

It should be documented in doc/lispref/sequences.texi, no?

As the intended use of length= is to compare lengths, it's confusing 
that it also accepts markers and floats, plus that makes the 
implementation a bit slower as it can't use EQ to compare lengths. It 
would be cleaner and simpler for length= to accept only sequences and 
integers, as Alexandria does.

I assume that markers and floats were put in only so that the 
byte-compiler could optimize expressions like (= (length FOO) BAR) 
without worrying about incompatibilities in the very-unlikely case where 
BAR is a float or a marker. In that case, perhaps the the byte-compiler 
should use a specialized length= function that is not visible to the 
user, so that the user-visible function (if any) can be kept cleaner.