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Improve ‘equal’ and array doc

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* doc/lispref/objects.texi (Array Type): Array sizes are
nonnegative fixnums, not arbitrary integers.
(Equality Predicates): Do not say that ‘eq’ equals ‘=’ on bignums.
Do not imply that ‘equal’ must signal an error on circular lists.
This commit is contained in:
Paul Eggert 2019-06-27 15:39:04 -07:00
parent 2212ab5035
commit bdbb390ffe
1 changed files with 9 additions and 6 deletions
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doc/lispref/objects.texi
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@ -964,7 +964,8 @@ char-tables.
A string is an array of characters and a vector is an array of
arbitrary objects. A bool-vector can hold only @code{t} or @code{nil}.
These kinds of array may have any length up to the largest integer.
These kinds of array may have any length up to the largest fixnum,
subject to system architecture limits and available memory.
Char-tables are sparse arrays indexed by any valid character code; they
can hold arbitrary objects.
@ -2085,7 +2086,7 @@ appropriate chapter describing the data type.
This function returns @code{t} if @var{object1} and @var{object2} are
the same object, and @code{nil} otherwise.
If @var{object1} and @var{object2} are integers with the same value,
If @var{object1} and @var{object2} are fixnums with the same value,
they are considered to be the same object (i.e., @code{eq} returns
@code{t}). If @var{object1} and @var{object2} are symbols with the
same name, they are normally the same object---but see @ref{Creating
@ -2095,7 +2096,7 @@ necessarily @code{eq} to each other: they are @code{eq} only if they
are the same object, meaning that a change in the contents of one will
be reflected by the same change in the contents of the other.
For other types of objects whose contents cannot be changed (e.g.,
floats), two arguments with the same contents might or might not be
bignums and floats), two arguments with the same contents might or might not be
the same object, and @code{eq} returns @code{t} or @code{nil}
depending on whether the Lisp interpreter created one object or two.
@ -2258,7 +2259,7 @@ However, two distinct buffers are never considered @code{equal}, even if
their textual contents are the same.
@end defun
The test for equality is implemented recursively; for example, given
For @code{equal}, equality is defined recursively; for example, given
two cons cells @var{x} and @var{y}, @code{(equal @var{x} @var{y})}
returns @code{t} if and only if both the expressions below return
@code{t}:
@ -2268,8 +2269,10 @@ returns @code{t} if and only if both the expressions below return
(equal (cdr @var{x}) (cdr @var{y}))
@end example
Because of this recursive method, circular lists may therefore cause
infinite recursion (leading to an error).
Comparing circular lists may therefore cause deep recursion that leads
to an error, and this may result in counterintuitive behavior such as
@code{(equal a b)} returning @code{t} whereas @code{(equal b a)}
signals an error.
@defun equal-including-properties object1 object2
This function behaves like @code{equal} in all cases but also requires