Commit db3874b1 authored by Basil L. Contovounesios's avatar Basil L. Contovounesios Committed by Paul Eggert

Refer to "proper lists" instead of "true lists"

* doc/lispref/lists.texi (Cons Cells, Building Lists):
* doc/lispref/sequences.texi (Vector Functions): Use the more
popular term "proper", rather than "true", to qualify nil-terminated
lists.

For discussion, see the following emacs-devel subthreads:
https://lists.gnu.org/archive/html/emacs-devel/2018-06/msg00112.html
https://lists.gnu.org/archive/html/emacs-devel/2018-06/msg00138.html
parent 35e0305d
......@@ -50,16 +50,19 @@ convention; at the level of cons cells, the @sc{car} and @sc{cdr}
slots have similar properties). Hence, the @sc{cdr} slot of each cons
cell in a list refers to the following cons cell.
@cindex proper list
@cindex true list
Also by convention, the @sc{cdr} of the last cons cell in a list is
@code{nil}. We call such a @code{nil}-terminated structure a
@dfn{true list}. In Emacs Lisp, the symbol @code{nil} is both a
symbol and a list with no elements. For convenience, the symbol
@code{nil} is considered to have @code{nil} as its @sc{cdr} (and also
as its @sc{car}).
Hence, the @sc{cdr} of a true list is always a true list. The
@sc{cdr} of a nonempty true list is a true list containing all the
@dfn{proper list}@footnote{It is sometimes also referred to as a
@dfn{true list}, but we generally do not use this terminology in this
manual.}. In Emacs Lisp, the symbol @code{nil} is both a symbol and a
list with no elements. For convenience, the symbol @code{nil} is
considered to have @code{nil} as its @sc{cdr} (and also as its
@sc{car}).
Hence, the @sc{cdr} of a proper list is always a proper list. The
@sc{cdr} of a nonempty proper list is a proper list containing all the
elements except the first.
@cindex dotted list
......@@ -71,10 +74,10 @@ Pair Notation}). There is one other possibility: some cons cell's
@sc{cdr} could point to one of the previous cons cells in the list.
We call that structure a @dfn{circular list}.
For some purposes, it does not matter whether a list is true,
For some purposes, it does not matter whether a list is proper,
circular or dotted. If a program doesn't look far enough down the
list to see the @sc{cdr} of the final cons cell, it won't care.
However, some functions that operate on lists demand true lists and
However, some functions that operate on lists demand proper lists and
signal errors if given a dotted list. Most functions that try to find
the end of a list enter infinite loops if given a circular list.
......@@ -522,7 +525,7 @@ object. The final argument is not copied or converted; it becomes the
is itself a list, then its elements become in effect elements of the
result list. If the final element is not a list, the result is a
dotted list since its final @sc{cdr} is not @code{nil} as required
in a true list.
in a proper list (@pxref{Cons Cells}).
@end defun
Here is an example of using @code{append}:
......
......@@ -1355,7 +1355,7 @@ each initialized to @var{object}.
@defun vconcat &rest sequences
@cindex copying vectors
This function returns a new vector containing all the elements of
@var{sequences}. The arguments @var{sequences} may be true lists,
@var{sequences}. The arguments @var{sequences} may be proper lists,
vectors, strings or bool-vectors. If no @var{sequences} are given,
the empty vector is returned.
......
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