I'm trying to install Facebook PHP SDK with Composer. This is what I get
$ composer install
Loading composer repositories with package information
Installing dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.
- Installation request for facebook/php-sdk dev-master -> satisfiable by facebook/php-sdk[dev-master].
- facebook/php-sdk dev-master requires ext-curl * -> the requested PHP extension curl is missing from your system.
$ php -m
This is caused because you don't have a library php5-curl installed in your system,
On Ubuntu its just simple run the line code below, in your case on Xamp take a look in Xamp documentation
sudo apt-get install php5-curl