Binding Actual Values to Formal Arguments

In order to implement the e operator for evaluating λ-expression bodies within the LISP Interpreter, we must devise a mechanistic way to bind actual arguments to formal arguments and to honor the contexts thus established during the time that a related λ-expression is being evaluated. There are several ways to do this. The earliest approach, which was employed in the original LISP Interpreter for the IBM 704 and 709, was to maintain a so-called association list. It is convenient to describe this approach and then use it as a model to explain how a LISP Interpreter works in effect, if not in fact.