$ from Okasaki's dissertation

gistfile1.rkt

#lang racket

(require (for-syntax syntax/parse))

(define-match-expander $
  (λ (stx)
    (syntax-parse stx
      [(_ pat ...)
       #'(app force pat ...)])))

;; error
#;
(match (delay 5)
    [5 'foo])

;; matches
(match (delay 5)
  [($ 5) 'foo])

;; if $ were primitive
(define (my-force x)
  (match x [($ x) x]))