Lisp - Returning Value from Function

By default, a function in LISP returns the value of the last expression evaluated as the return value. The following example would demonstrate this.

Example

Create a new source code file named main.lisp and type the following code in it.

main.lisp

; define a function add-all which will return sum of passed numbers
(defun add-all(a b c d)
   (+ a b c d)
)
; set sum as result of add-all function
(setq sum (add-all 10 20 30 40))
; print value of sum
(write sum)
; terminate printing
(terpri)
; print value of result of add-all function
(write (add-all 23.4 56.7 34.9 10.0))

Output

When you execute the code, it returns the following result −

100
125.0

However, you can use the return-from special operator to immediately return any value from the function.

Example

Update the source code file named main.lisp and type the following code in it −

main.lisp

; define a function to return a number as 10
(defun myfunc (num)
   (return-from myfunc 10)
   num
)
; print result of function call
(write (myfunc 20))

Output

When you execute the code, it returns the following result −

10

Change the code a little −

main.lisp

; define a function to return a number as 10
(defun myfunc (num)
   (return-from myfunc 10)
   write num
)
; print result of function call
(write (myfunc 20))

Output

It still returns −

10