When to use (values ...) (define-values ...) in Scheme
I have read documentation for functions such as values and define-val开发者_开发问答ues that return and consume multiple values. I understand what they do. It's not clear to me when you would want to use such a thing.
When would it be bad/impossible to build a single list of values and consume that single list of values instead?
define-values is a convenience that lets you directly bind variables to the results of a expression. It saves you some typing as you don't have to explicitly unpack a list. I don't think there are situations where it is bad or impossible to build a single list of values. In fact, that will be more portable than define-values.
Here is my original post on the topic; it is copied below.
In this thread in comp.lang.scheme the means to return multiple values are discussed. There are seemingly 3 solutions in R6RS:
(import (rnrs))
; let-values + values
(define (foo1)
(values 1 2 3))
(let-values (((a b c) (foo1)))
(display (list a b c))
(newline))
; cps
(define (foo2 k)
(k 1 2 3))
(foo2 (lambda (a b c)
(display (list a b c))
(newline)))
; list
(define (foo3)
(list 1 2 3))
(let ((result (foo3)))
(display result)
(newline))
Per Aziz and Aaron’s point; you should use the approach that communicates the most information to the reader.
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