[racket] About genericity...

I wanted to try it out, but it’s giving me an error about car expecting a pair:

. . car: contract violation
  expected: pair?
  given: #<flat-contract: (listof vector?)>

#lang racket

(require (submod def-multi/def-multi multim))
(require plot/utils)
(require (only-in racket [+ rkt:+]))
(require rackunit)

(def-multi +)

(add-multi + '() (lambda () 0))
(add-multi + (listof number?) (lambda args (apply + args)))
(add-multi + (listof vector?) (lambda args (apply v+ args)))

(check-equal? (+ 1 2 3) 6)
(check-equal? (+ (vector 1 2 3)
                 (vector 2 3 4)
                 (vector 3 4 5))
              (vector 6 9 12))



On Apr 4, 2014, at 11:23 AM, Patrick Useldinger <uselpa.list at gmail.com> wrote:

> On 02/04/2014 20:48, Patrick Useldinger wrote:
> 
>> I can share it if you're interested, it's roughly 40 lines of code.
> 
> Here's the link: https://github.com/uselpa/def-multi
> 
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