Non-deterministic Lambda Syntax Implemented in Racket

nd_lambda.rkt

#lang racket

(define *ambitions* '())

(define (nd-choice n)
  (let/cc return
    (for ((i (in-range n)))
      (let/cc cont
        (set! *ambitions* (cons cont *ambitions*))
        (return i))
      (set! *ambitions* (cdr *ambitions*)))
    n))

(define-syntax nd-lambda
  (syntax-rules ()
    ((_ (args ...) body ...)
     (begin
       (set! *ambitions* '())
       (lambda (args ...)
         (let ((result (begin body ...)))
           (cond
             (result result)
             ((null? *ambitions*) #f)
             (else ((car *ambitions*))))))))))


;;;
;;; EXAMPLE
;;;

(define >=7
  (nd-lambda (n) (= (nd-choice n) 7)))

(>=7 5)  ;=> #f
(>=7 10) ;=> #t