use Foo;
if (Foo->VERSION() < 1.56) {
    # do something...
}
# or
if ($Foo::VERSION < 1.56) {
    # do something...
}

##</code><code>##

use Foo 1.56 # Die during compiletime if the minimum version is not met.

##</code><code>##

perl -MList::Util -E 'say List::Util->VERSION()'