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Minor fixes in documentation of shorthands

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* etc/NEWS:
* doc/lispref/symbols.texi (Symbol Components, Creating Symbols)
(Shorthands): Improve wording, fix indexing and typos.
This commit is contained in:
Eli Zaretskii 2021-09-27 09:37:33 +03:00
parent 00011c0ad2
commit 106a95c8ab
2 changed files with 78 additions and 75 deletions
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139
doc/lispref/symbols.texi
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@ -70,9 +70,10 @@ important not to have two symbols with the same name. The Lisp reader
ensures this: every time it reads a symbol, it looks for an existing
symbol with the specified name before it creates a new one. To get a
symbol's name, use the function @code{symbol-name} (@pxref{Creating
Symbols}). Nonwithstanding each symbol having only one unique _print
name_, it is nevertheless possible to refer to that same symbol via
different terms called ``shorthands'' (@pxref{Shorthands}).
Symbols}). However, although each symbol has only one unique
@emph{print name}, it is nevertheless possible to refer to that same
symbol via different alias names called ``shorthands''
(@pxref{Shorthands}).
The value cell holds a symbol's value as a variable, which is what
you get if the symbol itself is evaluated as a Lisp expression.
@ -176,36 +177,34 @@ know how Lisp reads them. Lisp must ensure that it finds the same
symbol every time it reads the same sequence of characters in the same
context. Failure to do so would cause complete confusion.
When the Lisp reader encounters a reference to symbol in the source
code, it reads all the characters of that name. Then it looks up that
name in a table called an @dfn{obarray} to find the symbol that the
programmer meant.
@cindex symbol name hashing
@cindex hashing
@cindex obarray
@cindex bucket (in obarray)
One the techniques used in this lookup is called hashing, an efficient
method of looking something up. For example, instead of searching a
telephone book cover to cover when looking up Jan Jones, you start
with the J's and go from there. That is a simple version of hashing.
Each element of the obarray is a @dfn{bucket} which holds all the
symbols with a given hash code; to look for a given name, it is
sufficient to look through all the symbols in the bucket for that
name's hash code. (The same idea is used for general Emacs hash
tables, but they are a different data type; see @ref{Hash Tables}.)
When the Lisp reader encounters a name that references a symbol in
the source code, it reads all the characters of that name. Then it
looks up that name in a table called an @dfn{obarray} to find the
symbol that the programmer meant. The technique used in this lookup
is called ``hashing'', an efficient method of looking something up by
converting a sequence of characters to a number, known as a ``hash
code''. For example, instead of searching a telephone book cover to
cover when looking up Jan Jones, you start with the J's and go from
there. That is a simple version of hashing. Each element of the
obarray is a @dfn{bucket} which holds all the symbols with a given
hash code; to look for a given name, it is sufficient to look through
all the symbols in the bucket for that name's hash code. (The same
idea is used for general Emacs hash tables, but they are a different
data type; see @ref{Hash Tables}.)
@cindex shorthands
@cindex namespacing
@cindex namespaces
When looking up names, the reader also considers ``shorthands''. If
the programmer supplied them, this allows the reader to find a symbol
even if its name isn't typed out fully in the source code. Of course,
the reader needs to be aware of some pre-established context about
such shorthands, much as one needs context to be to able to refer
uniquely to Jan Jones by just the name ``Jan'': it's probably fine
when amongst the Joneses, or when Jan has been mentioned recently, but
very ambiguous in any other situation. @xref{Shorthands}.
When looking up names, the Lisp reader also considers ``shorthands''.
If the programmer supplied them, this allows the reader to find a
symbol even if its name isn't present in its full form in the source
code. Of course, the reader needs to be aware of some pre-established
context about such shorthands, much as one needs context to be to able
to refer uniquely to Jan Jones by just the name ``Jan'': it's probably
fine when amongst the Joneses, or when Jan has been mentioned
recently, but very ambiguous in any other situation.
@xref{Shorthands}.
@cindex interning
If a symbol with the desired name is found, the reader uses that
@ -220,11 +219,13 @@ same obarray. Thus, the reader gets the same symbols for the same
names, as long as you keep reading with the same obarray.
Interning usually happens automatically in the reader, but sometimes
other programs may want to do it. For example, a hypothetical
telephone book program could intern the name of each looked up
person's name as a symbol, even if the obarray did not contain it, so
that it could attach information to that new symbol such as the last
time someone looked it up.
other programs may want to do it. For example, after the @kbd{M-x}
command obtains the command name as a string using the minibuffer, it
then interns the string, to get the interned symbol with that name.
As another example, a hypothetical telephone book program could intern
the name of each looked up person's name as a symbol, even if the
obarray did not contain it, so that it could attach information to
that new symbol, such as the last time someone looked it up.
@cindex symbol equality
@cindex uninterned symbol
@ -232,7 +233,8 @@ time someone looked it up.
obarray. They are called @dfn{uninterned symbols}. An uninterned
symbol has the same four cells as other symbols; however, the only way
to gain access to it is by finding it in some other object or as the
value of a variable.
value of a variable. Uninterned symbols are sometimes useful in
generating Lisp code, see below.
In Emacs Lisp, an obarray is actually a vector. Each element of the
vector is a bucket; its value is either an interned symbol whose name
@ -256,8 +258,8 @@ not work---only @code{intern} can enter a symbol in an obarray properly.
@b{Common Lisp note:} Unlike Common Lisp, Emacs Lisp does not provide
for interning the same name in several different ``packages'', thus
creating multiple symbols with the same name but different packages.
Emacs Lisp provides a different namespacing system called shorthands
()
Emacs Lisp provides a different namespacing system called
``shorthands'' (@pxref{Shorthands}).
@end quotation
Most of the functions below take a name and sometimes an obarray as
@ -279,7 +281,7 @@ change the name of the symbol, but fails to update the obarray, so don't
do it!
@end defun
@cindex uninterned symbol (generated code)
@cindex uninterned symbol, and generating Lisp code
Creating an uninterned symbol is useful in generating Lisp code,
because an uninterned symbol used as a variable in the code you
generate cannot clash with any variables used in other Lisp programs.
@ -301,15 +303,14 @@ distinct uninterned symbol whose name is also @samp{foo}.
@defun gensym &optional prefix
This function returns a symbol using @code{make-symbol}, whose name is
made by appending @code{gensym-counter} to @var{prefix} and increnting
that counter, guaranteeing that no two calls to this function
generates a symbol with the same name. The prefix defaults to
made by appending @code{gensym-counter} to @var{prefix} and incrementing
that counter, guaranteeing that no two calls to this function will
generate a symbol with the same name. The prefix defaults to
@code{"g"}.
@end defun
@cindex uninterned symbol (recommendation for generated code)
To avoid problems when accidentally interning printed representation
of generated code, (@pxref{Printed Representation}), it is recommended
of generated code (@pxref{Printed Representation}), it is recommended
to use @code{gensym} instead of @code{make-symbol}.
@defun intern name &optional obarray
@ -638,60 +639,62 @@ functions. @xref{Defining Faces}.
@section Shorthands
@cindex shorthands
@cindex symbolic shorthands
@cindex namespacing
@cindex namespaces
@dfn{Shorthands}, sometimes known as "renamed symbols", are symbolic
forms found in Lisp source. They're just like regular symbolic forms,
except that when the Lisp reader encounters them, it produces symbols
which have a different and usually longer @dfn{print name}
(@pxref{Symbol Components}).
The symbol @dfn{shorthands}, sometimes known as ``renamed symbols'', are
symbolic forms found in Lisp source. They're just like regular
symbolic forms, except that when the Lisp reader encounters them, it
produces symbols which have a different and usually longer @dfn{print
name} (@pxref{Symbol Components}).
It is useful to think of shorthands as @emph{abbreviating} the full
names of intended symbols. Despite this, do not confuse with the
names of intended symbols. Despite this, do not confuse shorthands with the
Abbrev system @pxref{Abbrevs}.
@cindex namespace etiquette
Shorthands make Emacs Lisp's namespacing etiquette easier to work
Shorthands make Emacs Lisp's @dfn{namespacing etiquette} easier to work
with. Since all symbols are stored in a single obarray
(@pxref{Creating Symbols}), programmers commonly prefix each symbol
name with the name of the library where it originates. For example,
the functions @code{text-property-search-forward} and
@code{text-property-search-backward} both belong to the
@code{text-property-search.el} library (@pxref{Loading}). By properly
@file{text-property-search.el} library (@pxref{Loading}). By properly
prefixing symbol names, one effectively prevents clashes between
similarly named symbols which belong to different libraries and do
similarly named symbols which belong to different libraries and thus do
different things. However, this practice commonly originates very
long symbols names, which are bothersome to type and read after a
while.
long symbols names, which are inconvenient to type and read after a
while. Shorthands solve these issues in a clean way.
@defvar elisp-shorthands
This variable is an alist whose elements have the form
This variable's value is an alist whose elements have the form
@code{(@var{shorthand-prefix} . @var{longhand-prefix})}. Each element
instructs the Lisp reader to read every symbol form which starts with
@var{shorthand-prefix} as if it started with @var{longhand-prefix}
instead.
This variable may only be set file-locally (@pxref{File Variables, ,
This variable may only be set in file-local variables (@pxref{File Variables, ,
Local Variables in Files, emacs, The GNU Emacs Manual}).
@end defvar
Take this excerpt from following example of a hypothetical string
Here's an example of shorthands usage in a hypothetical string
manipulating library @file{some-nice-string-utils.el}.
@example
@smalllisp
(defun some-nice-string-utils-split (separator s &optional omit-nulls)
"A match-data saving variation on `split-string'."
"A match-data saving variant of `split-string'."
(save-match-data (split-string s separator omit-nulls)))
(defun some-nice-string-utils-lines (s)
"Split string S into a list of strings on newline characters."
"Split string S at newline characters into a list of strings."
(some-nice-string-utils-split "\\(\r\n\\|[\n\r]\\)" s))
@end example
@end smalllisp
As can be seen, it's quite tedious to read or develop this code since
the symbol names to type are so long. We can use shorthands to good
effect here.
the symbol names to type are so long. We can use shorthands to
alleviate that.
@example
@lisp1
(defun snu-split (separator s &optional omit-nulls)
"A match-data saving variation on `split-string'."
(save-match-data (split-string s separator omit-nulls)))
@ -703,10 +706,10 @@ effect here.
;; Local Variables:
;; elisp-shorthands: (("snu-" . "some-nice-string-utils-"))
;; End:
@end example
@end lisp
Even though the two excerpts look different, they are quite identical
after Lisp reader is done with them. Both will lead to the very same
after the Lisp reader processes them. Both will lead to the very same
symbols being interned (@pxref{Creating Symbols}). Thus loading or
byte-compiling any of the two files has equivalent results. The
shorthands @code{snu-split} and @code{snu-lines} used in the second
@ -720,9 +723,9 @@ Since @code{elisp-shorthands} is a file-local variable, it is possible
that multiple libraries depending on
@file{some-nice-string-utils-lines.el} refer to the same symbols under
@emph{different} shorthands, or not using shorthands at all. In the
next example, the @file{my-tricks.el} library refers to symbol
aforementioned symbol @code{some-nice-string-utils-lines} using the
@code{sns-} prefix.
next example, the @file{my-tricks.el} library refers to the
symbol @code{some-nice-string-utils-lines} using the
@code{sns-} prefix instead of @code{snu-}.
@example
(defun t-reverse-lines (s) (string-join (reverse (sns-lines s)) "\n")

14
etc/NEWS
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@ -3907,15 +3907,15 @@ It can be used to create Lisp strings with arbitrary byte sequences
(a.k.a. "raw bytes").
+++
** Shorthands
** Shorthands for Lisp symbols.
Shorthands are a general purpose namespacing system to make Emacs
Lisp's symbol-naming etiquette easier to manage. Also known as a
Lisp's symbol-naming etiquette easier to use. Also known as a
"renamed symbol", a shorthand is any symbolic form found in Lisp
source that abbreviates a symbol with a different and longer print
name. Among other applications, it facilitates the importation of
popular libraries such as 's.el' without the polution associated of
very short prefixes. For details, see the manual section "(elisp)
Shorthands".
source that "abbreviates" a symbol's print name with. Usually, the
abbreviated name will be shorter, but that is not necessarily so; this
feature could also be used for providing namespace prefixes to
symbols, in order to avoid name clashes and namespace pollution. For
details, see the manual section "(elisp) Shorthands".
+++
** New function 'string-search'.