#lang typed/racket

;;; dds/bn

;;; This module provides some quick definitions for running Boolean
;;; networks.  A Boolean network is a set of Boolean variables which
;;; are updated according to their corresponding update functions.
;;; The variables to be updated at each step are given by the mode.

(provide Variable State UpdateFunc Network
         update make-state make-bn)

(define-type Variable Symbol)

;;; A state of a Boolean network is a mapping from the variables of the
;;; network to their Boolean values.
(define-type State (HashTable Variable Boolean))

;;; An update function is a Boolean function computing a Boolean value
;;; from the given state.
(define-type UpdateFunc (-> State Boolean))

;;; A Boolean network is a mapping from its variables to its update
;;; functions.
(define-type Network (HashTable Variable UpdateFunc))

;;; Given a state s updates all the variables from xs.  This
;;; corresponds to a parallel mode.
(: update (-> Network State (Listof Variable) State))
(define (update bn  ; the Boolean network
                s   ; the state to operate on
                xs) ; the variables to update
  (let ([new-s : State (hash-copy s)])
    (for ([x xs])
      (let ([f (hash-ref bn x)])
        (hash-set! new-s x (f s))))
    new-s))

;;; A version of make-hash restricted to creating Boolean states.
(: make-state (-> (Listof (Pairof Variable Boolean)) State))
(define (make-state mappings)
  (make-hash mappings))

;;; A version of make-hash restricted to creating Boolean networks.
(: make-bn (-> (Listof (Pairof Variable UpdateFunc)) Network))
(define (make-bn funcs)
  (make-hash funcs))