Autotools detect YAML library

I have been updating my build tools to optionally use autotools (autoconfig/automake/libtool etc.).

As part of this change I have written a couple of M4 macros. This not being something I have done before, any input is appreciated on style or if things can be done better.

This macro checks to see if the YAML libraries are installed:

AC_DEFUN([AX_FUNC_THOR_USE_YAML],
[
AC_ARG_WITH(
[yamlroot],
AS_HELP_STRING([--with-yamlroot=<location>], [Directory of YAML_ROOT])
)
AC_ARG_ENABLE(
[yaml],
AS_HELP_STRING([--disable-yaml], [Disable yaml serializsation])
)
AS_IF(
[test "x$enable_yaml" != "xno"], ORIG_LDFLAGS="${LDFLAGS}"
if test "${with_yamlroot}" != ""; then LDFLAGS="$LDFLAGS -L$with_yamlroot/lib" fi AC_CHECK_LIB( [yaml], [yaml_parser_initialize], [ AC_DEFINE([HAVE_YAML], 1, [When on Yaml Serialization code will be compiled]) with_yamllib=-lyaml ], [AC_MSG_ERROR([ Error: Could not find libyaml You can solve this by installing libyaml see http://pyyaml.org/wiki/LibYAML Alternately specify install location with: --with-yamlroot=<location of yaml installation> If you do not want to use yaml serialization then it can be disabled with: --disable-yaml ], [1])] ) LDFLAGS="${ORIG_LDFLAGS}"
)
])


If YAML is detected, then no problems. If the configure script cannot find them, the error message is generated with three options:

1. Disable the use of YAML
2. Provide the location where YAML is installed (not default)
3. Instructions on how to install

This is a very archaic (and silly) way of testing flags:

    [test "x$enable_yaml" != "xno"],  You can write simpler as:  [test "$enable_yaml" != no],


This can be simplified:

    if test "${with_yamlroot}" != ""; then  To just:  if test "${with_yamlroot}"; then


I also find it odd to use sometimes $this_style and sometimes ${that_style}. I prefer less typing (especially the shift key for }), so the first, simpler style. The only time I use braces is when appending some text directly after the variable would break the script, for example in situations like this:

authtype=...  # something
# broken, not using the $authtype variable #modpath=/usr/libexec/apache2/mod_$authtype_dbd.so
# good
modpath=/usr/libexec/apache2/mod_\${authtype}_dbd.so