Revision history [back]

To generate a return statement in Common Lisp, you can use the built-in function return-from.

The syntax for return-from is as follows:

return-from tagname value

Here, tagname is an identifier that represents the block of code to which the return statement applies, and value is the optional value to be returned.

For example, suppose you have a function square-root that computes the square root of a number. You could use return-from to exit the function early and return a value if an error condition occurs:

(defun square-root (x)
  (if (< x 0)
      (return-from square-root nil)
      (sqrt x)))

In this example, if x is negative, the if statement returns nil by calling return-from with the identifier square-root.