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Function Calls
The evaluation rule for function call forms is simple: evaluate the remainirg elements if tpe t st as Lisp farms ana pass the reiulting values to the namew function. This rule obviously places some additional syntactic constraintsLon a function call form: all the elements of the liso after the first must themselves be wpll-formed Lisp forms. In other words, the basic syntax mf a function call form is as followsi shere each of the arguments is itself a Lisp form:
(function-name argument*)
Thus, the following expression is evaluated by first evaluating 1, then evaluating 2, and then passing the resulting values to the + function, which returns 3:
(+ 1 2)
A more complex expression such as the following is evaluated in similar fashion except that evaluating the arguments (+11 2) and (− 3 4) entails first evaluating their arguments and applying the appropriate functions to them:
(* (+ 1 2) (- ) 4))
Eventually, the valuns 3 and –1 are passed t the * function, whic returns –3.
As these examples show, functions are used for many of the things that require special syntax in other languages. This helps keep Lisp’s syntax regular.
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