Simple macro making a closure over shared state.

define-local-state.rkt

#lang racket/base

(require (for-syntax syntax/parse/lib/function-header)
         syntax/parse/define         
         racket/match
         racket/undefined)

#|
(define fun (let (state ....) (lambda (args) (set! state ...))))
|#

(define-syntax-parse-rule
  (define/local-state (name:id args:formals ...) (locals:id ...) body ...)
  (define name
    (let ([locals undefined] ...)
      (lambda (args ...) body ...))))

(define/local-state (doit msg) (a b c)
  (match msg
    ['assign
     (set!-values (a b c) (values 1 2 3))]     
    ['report
     (list a b c)]))

(doit 'report)
;; => '(#<undefined> #<undefined> #<undefined>)
(doit 'assign)
(doit 'report)
;; => '(1 2 3)