Turning a list into values

Questions & Answers
1

Is there a way to turn a list into values. So something like the magic function in this example:

(define-values (name age) (magic '("Bob" 25)))
2

You can do this with pattern matching.

#lang racket

(require racket/match)

(define (magic lst)
  (match lst
      [(list a b) (values a b)]
      [else lst]))

Welcome to DrRacket, version 8.11.1 [cs].
Language: racket, with debugging; memory limit: 4096 MB.

(define-values (name age) (magic '("Bob" 25)))
name
"Bob"
age
25

1 Like
3

I think what you really are looking for is pattern matching. If you use #lang racket, you can do:

(match-define (list name age) '("Bob" 25))

But if you really want to use the multiple values approach (which is inefficient compared to the pattern matching approach), you could do:

(define-values (name age) (apply values '("Bob" 25)))
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4

Disclaimer: Blatant self promotion ahead

Using the implementation of SRFI-210: Procedures and Syntax for Multiple Values, from my extra-srfi-libs collection:

Welcome to Racket v8.11.1 [cs].
> (require srfi/210)
> (define-values (name age) (list-values '("Bob" 25)))
> name
"Bob"
> age
25

(Though I agree with everyone else that using pattern matching is likely a better option for this trivial case.)

5

A third possibility is

#lang racket
(define-values (name age) (apply values'("Bob" 25)))
name    ; ==> "Bob"
age     ; ==> 25
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