Example: IF-N-Z-P

Let us now try to create a macro that will evaluate an arithmetic expression and then, depending on whether the value was negative, zero, or positive, evaluate one of three corresponding expressions.

(defmacro if-n-z-p (numexpr negform zeroform posform)

(list 'cond

(list (list '< (eval numexpr) 0)

negform)

(list (list '= (eval numexpr) 0)

zeroform)

(list (list '> (eval numexpr) 0)

posform)

(list t '(print 'error)) ) )

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