3.2 Making declarations
restrictive-ftype declaration specifies both the argument types and the result types of a set of functions. While anftype declaration conditionally restricts the value type of a function, arestrictive-ftype declaration unconditionally restricts both the argument types and the value type of a function. It is an error if the arguments to the function are not of the specified type, and the Compiler might produce unexpected results. Therestrictive-ftype has the following form:
(declare (restrictive-ftype type function-name-1 function-name-2 ...))The following proclamation declares that the function times will only accept two fixnum arguments and will always return a fixnum value:
(defun times (x y) (* x y)) (proclaim '(restrictive-ftype (function (fixnum fixnum) fixnum) times))Thus, in the following code, all of the arithmetic operators can be compiled as fixnum operators without requiring any additional declarations:
(defun do-some-arithmetic (i j) (declare (fixnum i j)) (times (+ (times (* i j) (+ i j)) j) i))
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