decision-tables.clj

decision-tables.clj

;; http://en.wikipedia.org/wiki/Decision_tables
;; http://rosettacode.org/wiki/Decision_tables
;; this example is ported from the pico lisp example

(defn yes? [condition]
  (print (str (first condition) "? "))
  (flush)
  (loop [reply (read-line)]
    (cond
     (contains? #{"T" "Y" "YES" "Yes" "y" "yes" "true" "1"} reply) true
     (contains? #{"NIL" "N" "NO" "No" "n" "no" "false" "0"} reply) nil
     :else (do
             (println "Invalid input")
             (recur (read-line))))))

(defn extract
  "Returns all non-nil results of applyinig fn to args"
  [fn & args]
  (filter identity (apply (partial map fn) args)))

(defn pick
  "Returns the first non-nil result of applying fn to args"
  [fn & args]
  (first (apply (partial extract fn) args)))

(def conditions
  [["printer does not print"               true true true true  nil  nil  nil  nil]
   ["a red light is flashing"              true true  nil  nil true true  nil  nil]
   ["printer is unrecognised"              true  nil true  nil true  nil true  nil]])

(def actions
  [["check the power cable"                nil  nil true]
   ["check the printer-computer cable"     true  nil true]
   ["ensure printer software is installed" true  nil true  nil true  nil true]
   ["check/replace ink"                    true true  nil  nil true true]
   ["check for paper jam"                  nil true  nil true]])

(defn decide
  ([] (apply decide (doall (map yes? conditions))))
  ([& input]
     (extract #(and %1 %2)
              (apply (partial pick (fn [& args]
                                     (when (not (pick #(not= %1 %2)
                                                      input (first args)))
                                       (rest args))))
                     (concat conditions actions))
              (map first actions))))

;; : (decide)
;; Printer does not print? y
;; A red light is flashing? y
;; Printer is unrecognised? n
;; -> ("Check/replace ink" "Check for paper jam")

;; : (decide)
;; Printer does not print? n
;; A red light is flashing? y
;; Printer is unrecognised? y
;; -> ("Ensure printer software is installed" "Check/replace ink")

;; : (decide)
;; Printer does not print? n
;; A red light is flashing? n
;; Printer is unrecognised? n
;; -> NIL