ing with credit is permitted. To copy otherwise, to republish, to post on servers, to redistribute to lists, or to use any component of this work in other works whether directly or by incorporation via a link, requires prior specific permission and/or a fee. Permissions may be requested from Publications Dept, ACM Inc., 1515 Broadway, New York, NY 10036 USA, fax +1 (212) 869-0481, or permissions@acm.org. This research was supported by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Office of Naval Research under contract number N00014-75-C-0522. Author's present address: Computer Science Department, University of Rochester, Rochester, NY 14627. 1. Introduction A severe problem in Lisp 1.5 [6] systems is the amount of time required to access the value of a variable. This problem is compounded by Lisp's choice of "fluid" or "dynamic" scoping for nonlocal (free) variables, wherein a procedure's free variables are considered bound in the envi...