A library for set!-ing numbers. You shouldn't use this.

set!-num.rkt

#lang racket/base

(require
 (for-syntax
  racket/base
  syntax/parse)
 (rename-in
  racket/base
  [#%datum old-datum]
  [set! old-set!]))

(define number-map (make-hasheq))

(define-syntax (set! stx)
  (syntax-parse stx
    [(_ i:number v)
     #'(hash-set! number-map i v)]
    [(_ . stx) #'(old-set! . stx)]))

(define-syntax (#%datum stx)
  (syntax-parse stx
    [(_ . i:number)
     #'(hash-ref! number-map (old-datum . i) (old-datum . i))]
    [stx #'(old-datum . stx)]))

(module+ test
  (require rackunit)
  (check-equal? 5 5)
  (set! 5 6)
  (check-equal? 5 6))

Seems reasonable; added. Not sure how to get for to use this new interpretation of numbers as sequence by default, though...

Should probably add support for reals by making that sequence lazy.