abstract Problem class

main
Matthew Butterick 10 years ago
parent 13af8d1952
commit 1fc2cf6f44

@ -1,3 +1,44 @@
#lang racket/base
(require racket/class)
(provide (all-defined-out))
(define Problem
;; The abstract class for a formal problem. You should subclass this and
;; implement the method successor, and possibly __init__, goal_test, and
;; path_cost. Then you will create instances of your subclass and solve them
;; with the various search functions.
(class object%
(super-new)
(init-field initial [goal null])
;; The constructor specifies the initial state, and possibly a goal
;; state, if there is a unique goal. Your subclass's constructor can add
;; other arguments.
(abstract successor)
;; Given a state, return a sequence of (action, state) pairs reachable
;; from this state. If there are many successors, consider an iterator
;; that yields the successors one at a time, rather than building them
;; all at once. Iterators will work fine within the framework.
(define/public (goal_test state)
;; Return True if the state is a goal. The default method compares the
;; state to self.goal, as specified in the constructor. Implement this
;; method if checking against a single self.goal is not enough.
(and (equal? state goal) #t))
(define/public (path_cost c state1 action state2)
;; Return the cost of a solution path that arrives at state2 from
;; state1 via action, assuming cost c to get up to state1. If the problem
;; is such that the path doesn't matter, this function will only look at
;; state2. If the path does matter, it will consider c and maybe state1
;; and action. The default method costs 1 for every step in the path.
(add1 c))
(abstract value)
;; For optimization problems, each state has a value. Hill-climbing
;; and related algorithms try to maximize this value.
))
(provide (all-defined-out))
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