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(define-module (monad stack)
#:export (pop peek push)
#:use-module (monad)
#:use-module (monad state))
;;; 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
(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))))
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