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;;;; Show the three different ways to deal with multiple return values
(load-extension "./libexample" "scm_init_example_module")
;;; Multiple values as lists. By default, if more than one value is to
;;; be returned, a list of the values is created and returned. The
;;; procedure divide-l does so:
(let* ((quotient/remainder (divide-l 37 5))
;; divide-l returns a list of the two values, so get them:
(quotient (car quotient/remainder))
(remainder (cadr quotient/remainder)))
(display "37 divided by 5 is ")
(display quotient)
(display ", remainder ")
(display remainder)
(newline))
;;; Multiple values as vectors. You can get vectors instead of lists
;;; if you want:
(let* ((quotient-remainder-vector (divide-v 40 7))
;; divide-v returns a vector of two values, so get them:
(quotient (vector-ref quotient-remainder-vector 0))
(remainder (vector-ref quotient-remainder-vector 1)))
(display "40 divided by 7 is ")
(display quotient)
(display ", remainder ")
(display remainder)
(newline))
;;; Multiple values for multiple-value continuations. (The most
;;; elegant way.) You can get multiple values passed to the
;;; multiple-value continuation, as created by `call-with-values'.
(call-with-values (lambda ()
;; the "producer" procedure
(divide-mv 91 13))
(lambda (quotient remainder)
;; the "consumer" procedure
(display "91 divided by 13 is ")
(display quotient)
(display ", remainder ")
(display remainder)
(newline)))
;;; SRFI-8 has a very convenient macro for this construction:
(use-modules (srfi srfi-8))
;;; If your Guile is too old, you can define the receive macro yourself:
;;;
;;; (define-macro (receive vars vals . body)
;;; `(call-with-values (lambda () ,vals)
;;; (lambda ,vars ,@body)))
(receive (quotient remainder)
(divide-mv 111 19) ; the "producer" form
;; In the body, `quotient' and `remainder' are bound to the two
;; values.
(display "111 divided by 19 is ")
(display quotient)
(display ", remainder ")
(display remainder)
(newline))
(exit 0)
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