This class represents a lambda-message-send, i.e. it keeps all what a message send needs: receiver, selector, arguments. any of its slots can be a free variable or, in own turn, be another lambda and so on, without any limitations.
are you aware of this: http://www.zogotounga.net/comp/squeak/functionaltalk.htm
... one of my mostly unnoticed contribution to Squeak :)
Stef