Lisp Written in Lisp

An interpreter is a program that reads another program and executes it, one step at a time. An attractive feature of Lisp is that a Lisp interpreter can easily be written in Lisp itself.

The basic functions performed by a Lisp interpreter include:

• Evaluating basic forms directly.

• Maintaining the binding environment that links variables with their values.

• Dispatching control to programs that evaluate different Lisp forms.

The top level of Lisp could be expressed simply as:

(do () (#f)
  (display "> ")
  (write (eval (read)))
  (newline) )

The interpreter given below is somewhat like the one in McCarthy's Lisp 1.5 manual; it allows ordinary Scheme code to be interpreted.

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