For full documentation, see: http://nikodemus.github.com/pileup/ Pileup is a portable, performant, and thread-safe binary heap for Common Lisp, under an MIT-style licence. It depends on Alexandria, and outside SBCL additionally on Bordeaux-Threads. Pileup is maintained in Git: git clone git://github.com/nikodemus/pileup.git will get you a local copy. http://github.com/nikodemus/pileup is the GitHub project page.