Yaf doesn't support PHP 5.6!

You may see this:

Warning: PHP Startup: yaf: Unable to initialize module

Module compiled with module API=20121212

PHP    compiled with module API=20131226

 

/Applications/MAMP/bin/php/php5.5.18/bin/pecl install yaf

 

sudo ln -s /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk/usr/include /Applications/MAMP/bin/php/php5.5.18/include