m4: Improved capitalize
17.7 Solution for 'capitalize'
==============================
The 'capitalize' macro (⇒Patsubst) as presented earlier does not
allow clients to follow the quoting rule of thumb. Consider the three
macros 'active', 'Active', and 'ACTIVE', and the difference between
calling 'capitalize' with the expansion of a macro, expanding the result
of a case change, and changing the case of a double-quoted string:
$ m4 -I examples
include(`capitalize.m4')dnl
define(`active', `act1, ive')dnl
define(`Active', `Act2, Ive')dnl
define(`ACTIVE', `ACT3, IVE')dnl
upcase(active)
=>ACT1,IVE
upcase(`active')
=>ACT3, IVE
upcase(``active'')
=>ACTIVE
downcase(ACTIVE)
=>act3,ive
downcase(`ACTIVE')
=>act1, ive
downcase(``ACTIVE'')
=>active
capitalize(active)
=>Act1
capitalize(`active')
=>Active
capitalize(``active'')
=>_capitalize(`active')
define(`A', `OOPS')
=>
capitalize(active)
=>OOPSct1
capitalize(`active')
=>OOPSctive
First, when 'capitalize' is called with more than one argument, it
was throwing away later arguments, whereas 'upcase' and 'downcase' used
'$*' to collect them all. The fix is simple: use '$*' consistently.
Next, with single-quoting, 'capitalize' outputs a single character, a
set of quotes, then the rest of the characters, making it impossible to
invoke 'Active' after the fact, and allowing the alternate macro 'A' to
interfere. Here, the solution is to use additional quoting in the
helper macros, then pass the final over-quoted output string through
'_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
'_capitalize' 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
'patsubst'. 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 'changequote' (⇒
Changequote). By changing the active quoting characters, we can
guarantee that replacement text injected by '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 'changequote'.
In the fixed version below, (also shipped as
'm4-1.4.18/examples/capitalize2.m4'), 'capitalize' uses the alternate
quotes of '<<[' and ']>>' (the longer strings are chosen so as to be
less likely to appear in the text being converted). The helpers
'_to_alt' and '_from_alt' merely reduce the number of characters
required to perform a 'changequote', since the definition changes twice.
The outermost pair means that 'patsubst' and '_capitalize_alt' are
invoked with alternate quoting; the innermost pair is used so that the
third argument to 'patsubst' can contain an unbalanced ']>>'/'<<[' pair.
Note that 'upcase' and 'downcase' must be redefined as '_upcase_alt' and
'_downcase_alt', since they contain nested quotes but are invoked with
the alternate quoting scheme in effect.
$ 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; `active'; ``active''; ```actIVE''')
=>Act1,Ive; Act2, Ive; Active; `Active'
undivert(`capitalize2.m4')dnl
=>divert(`-1')
=># upcase(text)
=># downcase(text)
=># capitalize(text)
=># change case of text, improved version
=>define(`upcase', `translit(`$*', `a-z', `A-Z')')
=>define(`downcase', `translit(`$*', `A-Z', `a-z')')
=>define(`_arg1', `$1')
=>define(`_to_alt', `changequote(`<<[', `]>>')')
=>define(`_from_alt', `changequote(<<[`]>>, <<[']>>)')
=>define(`_upcase_alt', `translit(<<[$*]>>, <<[a-z]>>, <<[A-Z]>>)')
=>define(`_downcase_alt', `translit(<<[$*]>>, <<[A-Z]>>, <<[a-z]>>)')
=>define(`_capitalize_alt',
=> `regexp(<<[$1]>>, <<[^\(\w\)\(\w*\)]>>,
=> <<[_upcase_alt(<<[<<[\1]>>]>>)_downcase_alt(<<[<<[\2]>>]>>)]>>)')
=>define(`capitalize',
=> `_arg1(_to_alt()patsubst(<<[<<[$*]>>]>>, <<[\w+]>>,
=> _from_alt()`]>>_$0_alt(<<[\&]>>)<<['_to_alt())_from_alt())')
=>divert`'dnl
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