An alternative dynamic binding model: deep binding with cacheing

The two most common dynamic binding models used in Lisp systems are shallow and deep binding. For a succinct summery of these see Padget and Fitch [1985], which includes a proposed third model. It is often claimed that shallow binding are unsuited to systems which allow context switching. We wish to describe an alternative binding model, deep binding with cacheing, which provides the efficiency of shallow binding in "ordinary" call/return control, while exhibiting the ease of context switching of deep binding. This binding model was implemented in the Lisp system built at the IBM Research Center, later elaborated into LISP/VM. In this article the term LISP/VM will be used to encompass both that program and all of its progenitors developed at IBM Research.