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Re: [PATCH] Add new lisp function length= with bytecode support
From: |
Paul Eggert |
Subject: |
Re: [PATCH] Add new lisp function length= with bytecode support |
Date: |
Mon, 27 Feb 2017 15:06:31 -0800 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 |
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.