gistfile1.rkt

#lang racket
(define ns (make-base-namespace))
(namespace-attach-module (current-namespace) ''#%builtin ns)

(define args (contract (vectorof string?) (vector "a") 'pos 'neg))

(parameterize ([current-namespace ns])
  (define current-args
    (namespace-variable-value 'current-command-line-arguments ns))
  (parameterize ([current-args args])
    args))

Gives error:

current-command-line-arguments: contract violation
expected: (vectorof string?)
given: '#("a")