Python struct hack in Common Lisp written by Death (see https://gist.github.com/266945) Modified to use ieee-floats instead of sb-kernel to increase compatibility. Tested on SBCL linux, windows and CLISP windows. pack spec &rest args => array Packs arguments according to spec as an octet buffer (simple array with 8-bit unsigned bytes). The spec string should be formatted as given in http://docs.python.org/library/struct.html#byte-order-size-and-alignment pack-into spec stream &rest args => stream Packs arguments according to spec into stream, which should obey the stream struct protocol, i.e. a specialized method struct-stream-protocol should exist for the stream. See below. unpack spec stream => list Unpacks bytes from stream according to spec and returns them in a list. calc-size spec => size Calculates and returns the size (in octets) that the spec specifies. struct-stream-protocol stream => reader writer A method for the stream object returning reader and writer functions. For an arbitrary object, these should be closures over that object. The reader function should return the current octet in the object and increment its position by one. It takes no arguments. The writer function should write the given octet to the object and increment its position by one. See this example from the pack.lisp source, which ensures vectors can be used as streams for the pack-into and unpack functions: (defmethod struct-stream-protocol ((vector vector)) (values (let ((i 0)) (lambda () (prog1 (aref vector i) (incf i)))) (let ((i 0)) (lambda (octet) (setf (aref vector i) octet) (incf i)))))