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Minor fixups for mutability doc

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* doc/lispref/objects.texi (Mutability): Minor fixups in
response to a comment by Dmitry Gutov (Bug#40671#477).
This commit is contained in:
Paul Eggert 2020-05-16 18:16:23 -07:00
parent 6ac2326e5b
commit b48ab743a8
1 changed files with 7 additions and 8 deletions
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doc/lispref/objects.texi
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@ -2381,7 +2381,7 @@ that for two strings to be equal, they have the same text properties.
Some Lisp objects should never change. For example, the Lisp
expression @code{"aaa"} yields a string, but you should not change
its contents. Indeed, some objects cannot be changed; for example,
its contents. And some objects cannot be changed; for example,
although you can create a new number by calculating one, Lisp provides
no operation to change the value of an existing number.
@ -2393,11 +2393,10 @@ point to somewhere else.
Although numbers never change and all markers are mutable,
some types have members some of which are mutable and others not. These
types include conses, vectors, and strings. For example,
although @code{"aaa"} yields a string that should not be changed,
@code{(make-string 3 ?a)} yields a mutable string that can be
changed via later calls to @code{aset}. Another example:
@code{(symbol-name 'cons)} yields a string @code{"cons"} that should
not be changed.
although @code{"cons"} and @code{(symbol-name 'cons)} both yield
strings that should not be changed, @code{(copy-sequence "cons")} and
@code{(make-string 3 ?a)} both yield mutable strings that can be
changed via later calls to @code{aset}.
A mutable object stops being mutable if it is part of an expression
that is evaluated. For example:
@ -2419,9 +2418,9 @@ becomes mutable afterwards.
changed, the resulting behavior is undefined: the Lisp interpreter
might signal an error, or it might crash or behave unpredictably in
other ways.@footnote{This is the behavior specified for languages like
Common Lisp and C, and it differs from the behavior of languages like
Common Lisp and C for constants, and this differs from languages like
JavaScript and Python where an interpreter is required to signal an
error if a program attempts to change a constant. Ideally the Emacs
error if a program attempts to change an immutable object. Ideally the Emacs
Lisp interpreter will evolve in latter direction.}
When similar constants occur as parts of a program, the Lisp