1.3.3 Evaluation Notation

A Lisp expression that you can evaluate is called a form. Evaluating a form always produces a result, which is a Lisp object. In the examples in this manual, this is indicated with ‘⇒’:

(car '(1 2))
     ⇒ 1

You can read this as “(car '(1 2)) evaluates to 1”.

When a form is a macro call, it expands into a new form for Lisp to evaluate. We show the result of the expansion with ‘→’. We may or may not show the actual result of the evaluation of the expanded form.

(news-cadr '(a b c))
     → (car (cdr '(a b c)))
     ⇒ b

Sometimes to help describe one form we show another form that produces identical results. The exact equivalence of two forms is indicated with ‘≡’.

(cons 'a nil) ≡ (list 'a)