Toronto and Houston make ten player trade

Well, this was unexpected. From the official Blue Jays Twitter feed:

Blue Jays complete 10 player trade with Astros. Major Leaguers Happ and Lyon to Toronto, Cordero and Francisco to Astros. Snider recalled

— Blue Jays-Official(@BlueJays) July 20, 2012

Jon Paul Morosi has the complete details:

Lyon, Happ, D. Carpenter for Cordero, B. Francisco and 4 minor leaguers (Carlos Perez, Asher Wojciechowski, David Rollins, Joseph Musgrove)

— Jon Morosi (@jonmorosi) July 20, 2012

I don't really understand this deal. I'm not sure why Toronto is giving up a bunch of minor leaguers for Lyon, who is a free agent after this season; J.A. Happ, who isn't good; and David Carpenter.