Changes to m4/doc/m4.texinfo,v

[Eric Blake]

CVSROOT:        /sources/m4
Module name:    m4
Changes by:     Eric Blake <ericb>      07/10/02 22:20:03

Index: doc/m4.texinfo
===================================================================
RCS file: /sources/m4/m4/doc/m4.texinfo,v
retrieving revision 1.112
retrieving revision 1.113
diff -u -b -r1.112 -r1.113
--- doc/m4.texinfo      1 Oct 2007 22:44:00 -0000       1.112
+++ doc/m4.texinfo      2 Oct 2007 22:20:02 -0000       1.113
@@ -289,6 +289,7 @@
 * Improved forloop::            Solution for @code{forloop}
 * Improved foreach::            Solution for @code{foreach}
 * Improved cleardivert::        Solution for @code{cleardivert}
+* Improved capitalize::         Solution for @code{capitalize}
 * Improved fatal_error::        Solution for @code{fatal_error}
 
 How to make copies of the overall M4 package
@@ -6047,18 +6048,47 @@
 word to upper case and the remaining characters to lower case.
 @end deffn
 
+First, an example of their usage, using implementations distributed in
address@hidden@value{VERSION}/@/examples/@/capitalize.m4}.
+
address@hidden examples
 @example
-define(`upcase', `translit(`$*', `a-z', `A-Z')')dnl
-define(`downcase', `translit(`$*', `A-Z', `a-z')')dnl
-define(`capitalize1',
-       `regexp(`$1', `^\(\w\)\(\w*\)',
-               `upcase(`\1')`'downcase(`\2')')')dnl
-define(`capitalize',
-       `patsubst(`$1', `\w+', `capitalize1(`\&')')')dnl
+$ @kbd{m4 -I examples}
+include(`capitalize.m4')
address@hidden
+upcase(`GNUs not Unix')
address@hidden NOT UNIX
+downcase(`GNUs not Unix')
address@hidden not unix
 capitalize(`GNUs not Unix')
 @result{}Gnus Not Unix
 @end example
 
+Now for the implementation.  There is a helper macro @code{_capitalize}
+which puts only its first word in mixed case.  Then @code{capitalize}
+merely parses out the words, and replaces them with an invocation of
address@hidden  (As presented here, the @code{capitalize} macro has
+some subtle flaws.  You should try to see if you can find and correct
+them; or @pxref{Improved capitalize, , Answers}).
+
address@hidden examples
address@hidden
+$ @kbd{m4 -I examples}
+undivert(`capitalize.m4')dnl
address@hidden(`-1')
address@hidden upcase(text)
address@hidden downcase(text)
address@hidden capitalize(text)
address@hidden   change case of text, simple version
address@hidden(`upcase', `translit(`$*', `a-z', `A-Z')')
address@hidden(`downcase', `translit(`$*', `A-Z', `a-z')')
address@hidden(`_capitalize',
address@hidden       `regexp(`$1', `^\(\w\)\(\w*\)',
address@hidden               `upcase(`\1')`'downcase(`\2')')')
address@hidden(`capitalize', `patsubst(`$1', `\w+', `_$0(`\&')')')
address@hidden'dnl
address@hidden example
+
 If @var{resyntax} is given, @var{regexp} must be given according to
 the syntax chosen, though the default regular expression syntax
 remains unchanged for other invocations:
@@ -7943,6 +7973,7 @@
 * Improved forloop::            Solution for @code{forloop}
 * Improved foreach::            Solution for @code{foreach}
 * Improved cleardivert::        Solution for @code{cleardivert}
+* Improved capitalize::         Solution for @code{capitalize}
 * Improved fatal_error::        Solution for @code{fatal_error}
 @end menu
 
@@ -8250,6 +8281,131 @@
 @result{}
 @end example
 
address@hidden Improved capitalize
address@hidden Solution for @code{capitalize}
+
+The @code{capitalize} macro (@pxref{Patsubst}) as presented earlier does
+not allow clients to follow the quoting rule of thumb.  Consider the
+three macros @code{active}, @code{Active}, and @code{ACTIVE}, and the
+difference between calling @code{capitalize} with the expansion of a
+macro, expanding the result of a case change, and changing the case of a
+double-quoted string:
+
address@hidden examples
address@hidden
+$ @kbd{m4 -I examples}
+include(`capitalize.m4')dnl
+define(`active', `act1, ive')dnl
+define(`Active', `Act2, Ive')dnl
+define(`ACTIVE', `ACT3, IVE')dnl
+upcase(active)
address@hidden,IVE
+upcase(`active')
address@hidden, IVE
+upcase(``active'')
address@hidden
+downcase(ACTIVE)
address@hidden,ive
+downcase(`ACTIVE')
address@hidden, ive
+downcase(``ACTIVE'')
address@hidden
+capitalize(active)
address@hidden
+capitalize(`active')
address@hidden
+capitalize(``active'')
address@hidden(`active')
+define(`A', `OOPS')
address@hidden
+capitalize(active)
address@hidden
+capitalize(`active')
address@hidden
address@hidden example
+
+First, when @code{capitalize} is called with more than one argument, it
+was throwing away later arguments, whereas @code{upcase} and
address@hidden used @samp{$*} to collect them all.  The fix is simple:
+use @samp{$*} consistently.
+
+Next, with single-quoting, @code{capitalize} outputs a single character,
+a set of quotes, then the rest of the characters, making it impossible
+to invoke @code{Active} after the fact, and allowing the alternate macro
address@hidden to interfere.  Here, the solution is to use additional quoting
+in the helper macros, then pass the final over-quoted output string
+through @code{_arg1} to remove the extra quoting and finally invoke the
+concatenated portions as a single string.
+
+Finally, when passed a double-quoted string, the nested macro
address@hidden is never invoked because it ended up nested inside
+quotes.  This one is the toughest to fix.  In short, we have no idea how
+many levels of quotes are in effect on the substring being altered by
address@hidden  If the replacement string cannot be expressed entirely
+in terms of literal text and backslash substitutions, then we need a
+mechanism to guarantee that the helper macros are invoked outside of
+quotes.  In other words, this sounds like a job for @code{changequote}
+(@pxref{Changequote}).  By changing the active quoting characters, we
+can guarantee that replacement text injected by @code{patsubst} always
+occurs in the middle of a string that has exactly one level of
+over-quoting using alternate quotes; so the replacement text closes the
+quoted string, invokes the helper macros, then reopens the quoted
+string.  In turn, that means the replacement text has unbalanced quotes,
+necessitating another round of @code{changequote}.
+
+In the fixed version below, (also shipped as
address@hidden@value{VERSION}/@/examples/@/capitalize.m4}), @code{capitalize}
+uses the alternate quotes of @samp{<<[} and @samp{]>>} (the longer
+strings are chosen so as to be less likely to appear in the text being
+converted).  The helpers @code{_to_alt} and @code{_from_alt} merely
+reduce the number of characters required to perform a
address@hidden, since the definition changes twice.  The outermost
+pair means that @code{patsubst} and @code{_capitalize_alt} are invoked
+with alternate quoting; the innermost pair is used so that the third
+argument to @code{patsubst} can contain an unbalanced
address@hidden>>}/@samp{<<[} pair.  Note that @code{upcase} and @code{downcase}
+must be redefined as @code{_upcase_alt} and @code{_downcase_alt}, since
+they contain nested quotes but are invoked with the alternate quoting
+scheme in effect.
+
address@hidden examples
address@hidden
+$ @kbd{m4 -I examples}
+include(`capitalize2.m4')dnl
+define(`active', `act1, ive')dnl
+define(`Active', `Act2, Ive')dnl
+define(`ACTIVE', `ACT3, IVE')dnl
+define(`A', `OOPS')dnl
+capitalize(active)
address@hidden,Ive
+capitalize(`active')
address@hidden, Ive
+capitalize(``active'')
address@hidden
+capitalize(```actIVE''')
address@hidden'
+undivert(`capitalize2.m4')dnl
address@hidden(`-1')
address@hidden upcase(text)
address@hidden downcase(text)
address@hidden capitalize(text)
address@hidden   change case of text, improved version
address@hidden(`upcase', `translit(`$*', `a-z', `A-Z')')
address@hidden(`downcase', `translit(`$*', `A-Z', `a-z')')
address@hidden(`_arg1', `$1')
address@hidden(`_to_alt', `changequote(`<<[', `]>>')')
address@hidden(`_from_alt', `changequote(<<[`]>>, <<[']>>)')
address@hidden(`_upcase_alt', `translit(<<[$*]>>, <<[a-z]>>, <<[A-Z]>>)')
address@hidden(`_downcase_alt', `translit(<<[$*]>>, <<[A-Z]>>, <<[a-z]>>)')
address@hidden(`_capitalize_alt',
address@hidden  `regexp(<<[$1]>>, <<[^\(\w\)\(\w*\)]>>,
address@hidden    
<<[_upcase_alt(<<[<<[\1]>>]>>)_downcase_alt(<<[<<[\2]>>]>>)]>>)')
address@hidden(`capitalize',
address@hidden  `_arg1(_to_alt()patsubst(<<[<<[$*]>>]>>, <<[\w+]>>,
address@hidden    _from_alt()`]>>_$0_alt(<<[\&]>>)<<['_to_alt())_from_alt())')
address@hidden'dnl
address@hidden example
+
 @node Improved fatal_error
 @section Solution for @code{fatal_error}