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(emacs-lisp-intro.info)Strange Names

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Strange Names
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   The name of the `cons' function is not unreasonable: it is an
abbreviation of the word `construct'.  The origins of the names for
`car' and `cdr', on the other hand, are esoteric: `car' is an acronym
from the phrase `Contents of the Address part of the Register'; and
`cdr' (pronounced `could-er') is an acronym from the phrase `Contents
of the Decrement part of the Register'.  These phrases refer to
specific pieces of hardware on the very early computer on which the
original Lisp was developed.  Besides being obsolete, the phrases have
been completely irrelevant for more than 25 years to anyone thinking
about Lisp.  Nonetheless, although a few brave scholars have begun to
use more reasonable names for these functions, the old terms are still
in use.  In particular, since the terms are used in the Emacs Lisp
source code, we will use them in this introduction.