Requesting Evaluation

Evaluation of an s-expression can be explicitly requested using the function EVAL. (EVAL x) gives the result of evaluating the value of the expression x in the current execution context. That is, EVAL performs an extra level of evaluation. The argument of EVAL is evaluated once, and should return as its value some Lisp code; then EVAL causes that Lisp code to be evaluated.

                     = (A)

          '(* 3.14159 (EXPT RADIUS 2))))

                     =  314.159
EVAL and its relatives allow Lisp code to be part of a data structure; the code can be retrieved from the data structure and executed by calling EVAL.

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