;;; ;;; Time-stamp: <2008-06-19 21:11:59 noel> ;;; ;;; Copyright (C) 2005 by Noel Welsh. ;;; ;;; This library is free software; you can redistribute it ;;; and/or modify it under the terms of the GNU Lesser ;;; General Public License as published by the Free Software ;;; Foundation; either version 2.1 of the License, or (at ;;; your option) any later version. ;;; This library is distributed in the hope that it will be ;;; useful, but WITHOUT ANY WARRANTY; without even the ;;; implied warranty of MERCHANTABILITY or FITNESS FOR A ;;; PARTICULAR PURPOSE. See the GNU Lesser General Public ;;; License for more details. ;;; You should have received a copy of the GNU Lesser ;;; General Public License along with this library; if not, ;;; write to the Free Software Foundation, Inc., 59 Temple ;;; Place, Suite 330, Boston, MA 02111-1307 USA ;;; Author: Noel Welsh <noelwelsh@yahoo.com> ;; ;; ;; Commentary: #lang scheme/base (provide (all-defined-out)) ;; struct monad : any any (define-struct monad (value state) #:mutable) ;; compose : (monad-of 'a) ('a -> (monad-of 'b)) -> (monad-of 'b) (define (compose comp build-comp) (lambda (seed0) (let* ((seed1 (comp seed0)) (value (monad-value seed1))) ((build-comp value) seed1)))) ;; compose*: (monad-of 'a) ('a -> (monad-of 'b)) ... -> (monad-of 'b) (define (compose* monad . actions) (if (null? actions) monad (compose monad (lambda (value) (apply compose* ((car actions) value) (cdr actions)))))) ;; sequence : (monad-of 'a) (monad-of 'b) -> (monad-of 'b) (define (sequence monad-a monad-b) (compose monad-a (lambda (v) monad-b))) (define (sequence* monad . monads) (if (null? monads) monad (sequence monad (apply sequence* (car monads) (cdr monads)))))