a growing snippet

helpers.rkt

#lang racket
(provide (all-defined-out))

(define any? any/c)

(define (until p f)
  (define (go x)
    (match x
      [(? p x)  x]
      [_        (go (f x))]))
  go)

(define (split-to-pairs l)
  (cond [(empty? l)        empty]
        [(empty? (cdr l))  (list l)]
        [else              (cons (list (car l) (cadr l))
                                 (split-to-pairs (cddr l)))]))