* fwd-para while:: The forward motion @code{while} loop.
Counting: Repetition and Regexps
+@set COUNT-WORDS count-words-example
+@c Length of variable name chosen so that things still line up when expanded.
* Why Count Words::
-* count-words-region:: Use a regexp, but find a problem.
+* @value{COUNT-WORDS}:: Use a regexp, but find a problem.
* recursive-count-words:: Start with case of no words in region.
* Counting Exercise::
-The @code{count-words-region} Function
+The @code{@value{COUNT-WORDS}} Function
-* Design count-words-region:: The definition using a @code{while} loop.
-* Whitespace Bug:: The Whitespace Bug in @code{count-words-region}.
+* Design @value{COUNT-WORDS}:: The definition using a @code{while} loop.
+* Whitespace Bug:: The Whitespace Bug in @code{@value{COUNT-WORDS}}.
Counting Words in a @code{defun}
* Divide and Conquer::
* Words and Symbols:: What to count?
* Syntax:: What constitutes a word or symbol?
-* count-words-in-defun:: Very like @code{count-words}.
+* count-words-in-defun:: Very like @code{@value{COUNT-WORDS}}.
* Several defuns:: Counting several defuns in a file.
* Find a File:: Do you want to look at a file?
* lengths-list-file:: A list of the lengths of many definitions.
@menu
* Why Count Words::
-* count-words-region:: Use a regexp, but find a problem.
+* @value{COUNT-WORDS}:: Use a regexp, but find a problem.
* recursive-count-words:: Start with case of no words in region.
* Counting Exercise::
@end menu
-@node Why Count Words, count-words-region, Counting Words, Counting Words
+@node Why Count Words, @value{COUNT-WORDS}, Counting Words, Counting Words
@ifnottex
@unnumberedsec Counting words
@end ifnottex
-The standard Emacs distribution contains a function for counting the
-number of lines within a region. However, there is no corresponding
-function for counting words.
+The standard Emacs distribution contains functions for counting the
+number of lines and words within a region.
Certain types of writing ask you to count words. Thus, if you write
an essay, you may be limited to 800 words; if you write a novel, you
-may discipline yourself to write 1000 words a day. It seems odd to me
-that Emacs lacks a word count command. Perhaps people use Emacs
-mostly for code or types of documentation that do not require word
-counts; or perhaps they restrict themselves to the operating system
-word count command, @code{wc}. Alternatively, people may follow
-the publishers' convention and compute a word count by dividing the
-number of characters in a document by five. In any event, here are
-commands to count words.
-
-@node count-words-region, recursive-count-words, Why Count Words, Counting Words
+may discipline yourself to write 1000 words a day. It seems odd, but
+for a long time, Emacs lacked a word count command. Perhaps people used
+Emacs mostly for code or types of documentation that did not require
+word counts; or perhaps they restricted themselves to the operating
+system word count command, @code{wc}. Alternatively, people may have
+followed the publishers' convention and computed a word count by
+dividing the number of characters in a document by five.
+
+There are many ways to implement a command to count words. Here are
+some examples, which you may wish to compare with the standard Emacs
+command, @code{count-words-region}.
+
+@node @value{COUNT-WORDS}, recursive-count-words, Why Count Words, Counting Words
@comment node-name, next, previous, up
-@section The @code{count-words-region} Function
-@findex count-words-region
+@section The @code{@value{COUNT-WORDS}} Function
+@findex @value{COUNT-WORDS}
A word count command could count words in a line, paragraph, region,
or buffer. What should the command cover? You could design the
the Emacs tradition encourages flexibility---you may want to count
words in just a section, rather than all of a buffer. So it makes
more sense to design the command to count the number of words in a
-region. Once you have a @code{count-words-region} command, you can,
+region. Once you have a command to count words in a region, you can,
if you wish, count words in a whole buffer by marking it with
@w{@kbd{C-x h}} (@code{mark-whole-buffer}).
or to a @code{while} loop.
@menu
-* Design count-words-region:: The definition using a @code{while} loop.
-* Whitespace Bug:: The Whitespace Bug in @code{count-words-region}.
+* Design @value{COUNT-WORDS}:: The definition using a @code{while} loop.
+* Whitespace Bug:: The Whitespace Bug in @code{@value{COUNT-WORDS}}.
@end menu
-@node Design count-words-region, Whitespace Bug, count-words-region, count-words-region
+@node Design @value{COUNT-WORDS}, Whitespace Bug, @value{COUNT-WORDS}, @value{COUNT-WORDS}
@ifnottex
-@unnumberedsubsec Designing @code{count-words-region}
+@unnumberedsubsec Designing @code{@value{COUNT-WORDS}}
@end ifnottex
First, we will implement the word count command with a @code{while}
The name of the function should be self-explanatory and similar to the
existing @code{count-lines-region} name. This makes the name easier
-to remember. @code{count-words-region} is a good choice.
+to remember. @code{count-words-region} is the obvious choice. Since
+that name is now used for the standard Emacs command to count words, we
+will name our implementation @code{@value{COUNT-WORDS}}.
The function counts words within a region. This means that the
argument list must contain symbols that are bound to the two
count words, second, to run the @code{while} loop, and third, to send
a message to the user.
-When a user calls @code{count-words-region}, point may be at the
+When a user calls @code{@value{COUNT-WORDS}}, point may be at the
beginning or the end of the region. However, the counting process
must start at the beginning of the region. This means we will want
to put point there if it is not already there. Executing
@smallexample
@group
;;; @r{First version; has bugs!}
-(defun count-words-region (beginning end)
+(defun @value{COUNT-WORDS} (beginning end)
"Print number of words in the region.
Words are defined as at least one word-constituent
character followed by at least one character that
@noindent
As written, the function works, but not in all circumstances.
-@node Whitespace Bug, , Design count-words-region, count-words-region
+@node Whitespace Bug, , Design @value{COUNT-WORDS}, @value{COUNT-WORDS}
@comment node-name, next, previous, up
-@subsection The Whitespace Bug in @code{count-words-region}
+@subsection The Whitespace Bug in @code{@value{COUNT-WORDS}}
-The @code{count-words-region} command described in the preceding
+The @code{@value{COUNT-WORDS}} command described in the preceding
section has two bugs, or rather, one bug with two manifestations.
First, if you mark a region containing only whitespace in the middle
-of some text, the @code{count-words-region} command tells you that the
+of some text, the @code{@value{COUNT-WORDS}} command tells you that the
region contains one word! Second, if you mark a region containing
only whitespace at the end of the buffer or the accessible portion of
a narrowed buffer, the command displays an error message that looks
@smallexample
@group
;; @r{First version; has bugs!}
-(defun count-words-region (beginning end)
+(defun @value{COUNT-WORDS} (beginning end)
"Print number of words in the region.
Words are defined as at least one word-constituent character followed
by at least one character that is not a word-constituent. The buffer's
If you wish, you can also install this keybinding by evaluating it:
@smallexample
-(global-set-key "\C-c=" 'count-words-region)
+(global-set-key "\C-c=" '@value{COUNT-WORDS})
@end smallexample
To conduct the first test, set mark and point to the beginning and end
of the following line and then type @kbd{C-c =} (or @kbd{M-x
-count-words-region} if you have not bound @kbd{C-c =}):
+@value{COUNT-WORDS}} if you have not bound @kbd{C-c =}):
@smallexample
one two three
Repeat the test, but place mark at the beginning of the line and place
point just @emph{before} the word @samp{one}. Again type the command
-@kbd{C-c =} (or @kbd{M-x count-words-region}). Emacs should tell you
+@kbd{C-c =} (or @kbd{M-x @value{COUNT-WORDS}}). Emacs should tell you
that the region has no words, since it is composed only of the
whitespace at the beginning of the line. But instead Emacs tells you
that the region has one word!
@file{*scratch*} buffer and then type several spaces at the end of the
line. Place mark right after the word @samp{three} and point at the
end of line. (The end of the line will be the end of the buffer.)
-Type @kbd{C-c =} (or @kbd{M-x count-words-region}) as you did before.
+Type @kbd{C-c =} (or @kbd{M-x @value{COUNT-WORDS}}) as you did before.
Again, Emacs should tell you that the region has no words, since it is
composed only of the whitespace at the end of the line. Instead,
Emacs displays an error message saying @samp{Search failed}.
Consider the first manifestation of the bug, in which the command
tells you that the whitespace at the beginning of the line contains
-one word. What happens is this: The @code{M-x count-words-region}
+one word. What happens is this: The @code{M-x @value{COUNT-WORDS}}
command moves point to the beginning of the region. The @code{while}
tests whether the value of point is smaller than the value of
@code{end}, which it is. Consequently, the regular expression search
repeat count. (In Emacs, you can see a function's documentation by
typing @kbd{C-h f}, the name of the function, and then @key{RET}.)
-In the @code{count-words-region} definition, the value of the end of
+In the @code{@value{COUNT-WORDS}} definition, the value of the end of
the region is held by the variable @code{end} which is passed as an
argument to the function. Thus, we can add @code{end} as an argument
to the regular expression search expression:
(re-search-forward "\\w+\\W*" end)
@end smallexample
-However, if you make only this change to the @code{count-words-region}
+However, if you make only this change to the @code{@value{COUNT-WORDS}}
definition and then test the new version of the definition on a
stretch of whitespace, you will receive an error message saying
@samp{Search failed}.
than the value of end, since the @code{re-search-forward} expression
did not move point. @dots{} and the cycle repeats @dots{}
-The @code{count-words-region} definition requires yet another
+The @code{@value{COUNT-WORDS}} definition requires yet another
modification, to cause the true-or-false-test of the @code{while} loop
to test false if the search fails. Put another way, there are two
conditions that must be satisfied in the true-or-false-test before the
found, point is moved through the region. When the search expression
fails to find another word, or when point reaches the end of the
region, the true-or-false-test tests false, the @code{while} loop
-exits, and the @code{count-words-region} function displays one or
+exits, and the @code{@value{COUNT-WORDS}} function displays one or
other of its messages.
-After incorporating these final changes, the @code{count-words-region}
+After incorporating these final changes, the @code{@value{COUNT-WORDS}}
works without bugs (or at least, without bugs that I have found!).
Here is what it looks like:
@smallexample
@group
;;; @r{Final version:} @code{while}
-(defun count-words-region (beginning end)
+(defun @value{COUNT-WORDS} (beginning end)
"Print number of words in the region."
(interactive "r")
(message "Counting words in region ... ")
@end group
@end smallexample
-@node recursive-count-words, Counting Exercise, count-words-region, Counting Words
+@node recursive-count-words, Counting Exercise, @value{COUNT-WORDS}, Counting Words
@comment node-name, next, previous, up
@section Count Words Recursively
@cindex Count words recursively
You can write the function for counting words recursively as well as
with a @code{while} loop. Let's see how this is done.
-First, we need to recognize that the @code{count-words-region}
+First, we need to recognize that the @code{@value{COUNT-WORDS}}
function has three jobs: it sets up the appropriate conditions for
counting to occur; it counts the words in the region; and it sends a
message to the user telling how many words there are.
message; the other will return the word count.
Let us start with the function that causes the message to be displayed.
-We can continue to call this @code{count-words-region}.
+We can continue to call this @code{@value{COUNT-WORDS}}.
This is the function that the user will call. It will be interactive.
Indeed, it will be similar to our previous versions of this
@smallexample
@group
;; @r{Recursive version; uses regular expression search}
-(defun count-words-region (beginning end)
+(defun @value{COUNT-WORDS} (beginning end)
"@var{documentation}@dots{}"
(@var{interactive-expression}@dots{})
@end group
@smallexample
@group
-(defun count-words-region (beginning end)
+(defun @value{COUNT-WORDS} (beginning end)
"Print number of words in the region."
(interactive "r")
@end group
Note that the search expression is part of the do-again-test---the
function returns @code{t} if its search succeeds and @code{nil} if it
fails. (@xref{Whitespace Bug, , The Whitespace Bug in
-@code{count-words-region}}, for an explanation of how
+@code{@value{COUNT-WORDS}}}, for an explanation of how
@code{re-search-forward} works.)
The do-again-test is the true-or-false test of an @code{if} clause.
@smallexample
@group
;;; @r{Recursive version}
-(defun count-words-region (beginning end)
+(defun @value{COUNT-WORDS} (beginning end)
"Print number of words in the region.
@end group
Our next project is to count the number of words in a function
definition. Clearly, this can be done using some variant of
-@code{count-word-region}. @xref{Counting Words, , Counting Words:
+@code{@value{COUNT-WORDS}}. @xref{Counting Words, , Counting Words:
Repetition and Regexps}. If we are just going to count the words in
one definition, it is easy enough to mark the definition with the
@kbd{C-M-h} (@code{mark-defun}) command, and then call
-@code{count-word-region}.
+@code{@value{COUNT-WORDS}}.
However, I am more ambitious: I want to count the words and symbols in
every definition in the Emacs sources and then print a graph that
* Divide and Conquer::
* Words and Symbols:: What to count?
* Syntax:: What constitutes a word or symbol?
-* count-words-in-defun:: Very like @code{count-words}.
+* count-words-in-defun:: Very like @code{@value{COUNT-WORDS}}.
* Several defuns:: Counting several defuns in a file.
* Find a File:: Do you want to look at a file?
* lengths-list-file:: A list of the lengths of many definitions.
@noindent
However, if we mark the @code{multiply-by-seven} definition with
@kbd{C-M-h} (@code{mark-defun}), and then call
-@code{count-words-region} on it, we will find that
-@code{count-words-region} claims the definition has eleven words, not
+@code{@value{COUNT-WORDS}} on it, we will find that
+@code{@value{COUNT-WORDS}} claims the definition has eleven words, not
ten! Something is wrong!
-The problem is twofold: @code{count-words-region} does not count the
+The problem is twofold: @code{@value{COUNT-WORDS}} does not count the
@samp{*} as a word, and it counts the single symbol,
@code{multiply-by-seven}, as containing three words. The hyphens are
treated as if they were interword spaces rather than intraword
@samp{multiply by seven}.
The cause of this confusion is the regular expression search within
-the @code{count-words-region} definition that moves point forward word
-by word. In the canonical version of @code{count-words-region}, the
+the @code{@value{COUNT-WORDS}} definition that moves point forward word
+by word. In the canonical version of @code{@value{COUNT-WORDS}}, the
regexp is:
@smallexample
Usually, a hyphen is not specified as a `word constituent character'.
Instead, it is specified as being in the `class of characters that are
part of symbol names but not words.' This means that the
-@code{count-words-region} function treats it in the same way it treats
-an interword white space, which is why @code{count-words-region}
+@code{@value{COUNT-WORDS}} function treats it in the same way it treats
+an interword white space, which is why @code{@value{COUNT-WORDS}}
counts @samp{multiply-by-seven} as three words.
There are two ways to cause Emacs to count @samp{multiply-by-seven} as
constituent character; there are others, too.
Alternatively, we can redefine the regular expression used in the
-@code{count-words} definition so as to include symbols. This
+@code{@value{COUNT-WORDS}} definition so as to include symbols. This
procedure has the merit of clarity, but the task is a little tricky.
@need 1200
@cindex Counting words in a @code{defun}
We have seen that there are several ways to write a
-@code{count-word-region} function. To write a
+@code{count-words-region} function. To write a
@code{count-words-in-defun}, we need merely adapt one of these
versions.
How to test this? The function is not interactive, but it is easy to
put a wrapper around the function to make it interactive; we can use
almost the same code as for the recursive version of
-@code{count-words-region}:
+@code{@value{COUNT-WORDS}}:
@smallexample
@group
@itemize @bullet
@item
-Install the @code{count-words-region} function and then cause it to
+Install the @code{@value{COUNT-WORDS}} function and then cause it to
enter the built-in debugger when you call it. Run the command on a
region containing two words. You will need to press @kbd{d} a
remarkable number of times. On your system, is a `hook' called after
Manual}.)
@item
-Copy @code{count-words-region} into the @file{*scratch*} buffer,
+Copy @code{@value{COUNT-WORDS}} into the @file{*scratch*} buffer,
instrument the function for Edebug, and walk through its execution.
The function does not need to have a bug, although you can introduce
one if you wish. If the function lacks a bug, the walk-through
@item
In the Edebug debugging buffer, use the @kbd{p}
(@code{edebug-bounce-point}) command to see where in the region the
-@code{count-words-region} is working.
+@code{@value{COUNT-WORDS}} is working.
@item
Move point to some spot further down the function and then type the
@bye
-@ignore
- arch-tag: da1a2154-531f-43a8-8e33-fc7faad10acf
-@end ignore
projects / emacs.git / commitdiff