# Multiple Return Values (Lisp solution)

• I'm not trying to start a war over preferred languages, I just enjoy working through these problems in a variety of languages on my own time to keep my wit sharp, and this problem raised an interesting use case for multiple return values. Here is a solution in common lisp (it's O(sqrt(N)) time complexity and is more or less the algorithm most people seem to have produced here):

``````(defun sum-of-squares-p (i)
(loop with top = (1- (floor (sqrt i)))
for s from 1 upto top do
(multiple-value-bind (div remain)
(floor (sqrt (- i (* s s))))
(when (= remain 0)
(return-from sum-of-squares-p
(values t s div)))))
(values nil 0 0))
``````

The interesting thing about this solution is not the algorithm, which is much the same as other solutions here, but rather the return value - in a boolean or single-value context, it's either t (true) or nil (false), but because in Lisp a function can return multiple values, the integers one would sum and square are also returned, and can be used later. An example REPL session with the above defined:

``````CL-USER> (sum-of-squares-p 5)
T
1
2
CL-USER> (if (sum-of-squares-p 5) "Yep!" "Nah")
"Yep!"
CL-USER> (loop for i from 0 to 10 do
(multiple-values-bind (p a b) (sum-of-squares-p i)
(when p (format t "~A = ~A^2 + ~A^2~%" i a b))))
5 = 1^2 + 2^2
10 = 1^2 + 3^2
NIL
``````

I wanted to point it out as an interesting language feature. I wish more languages had this feature because it helps maintain abstraction boundaries in cases where subsequently useful values are a byproduct of whatever a function nominally computes.

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