Snappy Extension for PHP Formula was removed
Last version was
php56-snappy requires the following formulae to be installed:
autoconf 2.69 Automatic configure script builder
snappy 1.1.7_1 Compression/decompression library aiming for high speed

Recent formula history

ilovezfs php56: migrate to homebrew/core (#4835)
Andreas Braun Add description for snappy formula
Andy Blyler fix style issues
Andy Blyler php56-snappy: convert from sha1 to sha256
Jack Nagel Move abstract classes out of Formula directory

Formula code at GitHub