Restore the old behaviour of AC_LANG

[Pavel Roskin]

Hello!

AC_LANG used to expand to the language name (it wasn't documented). Now
AC_LANG doesn't work without arguments at all. It's time to restore the
old behaviour.

It's not exactly the old behaviour in the sence that 2 of 3 languages have
been renamed since then. Anyway, I cannot find a better name than AC_LANG
for this function. We shouldn't encourage people to use _AC_LANG.

ChangeLog:
        * aclang.m4 (AC_LANG): Expand to the current language name
        when called without arguments.
        * doc/autoconf.texi (Language Choice): Document it.

Regards,
Pavel Roskin

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Index: aclang.m4
--- aclang.m4   Fri Nov 10 20:29:31 2000
+++ aclang.m4   Fri Nov 10 21:25:11 2000
@@ -111,14 +111,18 @@
 # AC_LANG(LANG)
 # -------------
 # Set the current language to LANG.
+# Without arguments, expand to the current language.
 #
 # Do *not* write AC_LANG([$1]), because this pair of parens does not
 # correspond to an evaluation, rather, they are just part of the name.
 # If you add quotes here, they will be part of the name too, yielding
 # `AC_LANG([C])' for instance, which does not exist.
 AC_DEFUN([AC_LANG],
-[m4_define([_AC_LANG], [$1])dnl
-_AC_LANG_DISPATCH([$0], _AC_LANG, $@)])
+[ifval([$1],
+       [m4_define([_AC_LANG], [$1])dnl
+_AC_LANG_DISPATCH([$0], _AC_LANG, $@)],
+       [_AC_LANG]dnl
+)])
 
 
 # AC_LANG_PUSH(LANG)
Index: doc/autoconf.texi
--- doc/autoconf.texi   Fri Nov 10 20:29:37 2000
+++ doc/autoconf.texi   Fri Nov 10 21:28:01 2000
@@ -5980,9 +5980,10 @@
 features by default.  The following macros determine which language's
 compiler is used in tests that follow in @file{configure.in}.
 
address@hidden AC_LANG (@var{language})
address@hidden AC_LANG (@ovar{language})
 Do compilation tests using the compiler, preprocessor and file
-extensions for the @var{language}.
+extensions for the @var{language}.  If @var{language} is not specified,
+expand to the currently active language.
 
 Supported languages are:
 
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