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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 Some Lisp objects should never change. For example, the Lisp
expression @code{"aaa"} yields a string, but you should not change 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 although you can create a new number by calculating one, Lisp provides
no operation to change the value of an existing number. 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, Although numbers never change and all markers are mutable,
some types have members some of which are mutable and others not. These some types have members some of which are mutable and others not. These
types include conses, vectors, and strings. For example, types include conses, vectors, and strings. For example,
although @code{"aaa"} yields a string that should not be changed, although @code{"cons"} and @code{(symbol-name 'cons)} both yield
@code{(make-string 3 ?a)} yields a mutable string that can be strings that should not be changed, @code{(copy-sequence "cons")} and
changed via later calls to @code{aset}. Another example: @code{(make-string 3 ?a)} both yield mutable strings that can be
@code{(symbol-name 'cons)} yields a string @code{"cons"} that should changed via later calls to @code{aset}.
not be changed.
A mutable object stops being mutable if it is part of an expression A mutable object stops being mutable if it is part of an expression
that is evaluated. For example: that is evaluated. For example:
@ -2419,9 +2418,9 @@ becomes mutable afterwards.
changed, the resulting behavior is undefined: the Lisp interpreter changed, the resulting behavior is undefined: the Lisp interpreter
might signal an error, or it might crash or behave unpredictably in might signal an error, or it might crash or behave unpredictably in
other ways.@footnote{This is the behavior specified for languages like 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 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.} Lisp interpreter will evolve in latter direction.}
When similar constants occur as parts of a program, the Lisp When similar constants occur as parts of a program, the Lisp