;;; Commentary:
;; Simple stateful stack module for showing the state monad
;; in action. These functions assume that they are in a
;; (state list) monad. But dynamic types!
;;
;; TODO test these for empty stack
;;; Code:
(define-module (monad stack)
  #:export (pop peek push)
  #:use-module (monad)
  #:use-module (monad state))

(define (pop)
  (do st <- (get)
      let top = (car st)
      (put (cdr st))
      (return-state top)))

(define (peek)
  (do st <- (get)
      (return-state (car st))))

(define (push v)
  (do st <- (get)
      (put (cons v st))))