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;; Eliza, adapted from PAIP chapter 5
(ns #^{:doc "Eliza in Clojure"}
(:require [clojure.contrib.seq-utils :as seq-utils])
(:use [clojure.test]))
(def ^{:private true}
'(((?*x hello ?*y)
(How do you do. Please state your problem.))
((?*x I want ?*y)
(What would it mean if you got ?y ?)
(Why do you want ?y ?)
(Suppose you got ?y soon))
((?*x if ?*y)
(Do you really think it is likely that ?y ?)
(Do you wish that ?y ?)
(What do you think about ?y ?)
(Really? If ?y ?))
((?*x no ?*y)
(Why not?) (You are being rather negative.)
(Are you saying no just to be negative?))
((?*x I was ?*y)
(Were you really?) (Perhaps I already knew you were $y .)
(Why do you tell me you were ?y now?))
((?*x I feel ?*y)
(Do you often feel ?y ?))
((?*x I felt ?*y)
(What other feelings do you have?))
(I am not sure I understand.)
(Could you put that another way?)
(Go on.))))
(defn- pattern-variable?
"Is the argument a symbol that looks like a pattern variable?"
(and (symbol? x)
(.startsWith (name x) "?")
(> (.length (name x)) 1)))
(deftest test-pattern-variable?
(is (pattern-variable? '?x))
(is (pattern-variable? '?1))
(is (pattern-variable? '?xy))
(is (pattern-variable? '?1-2))
(is (not (pattern-variable? 'a)))
(is (not (pattern-variable? 'x?)))
(is (not (pattern-variable? '(?x))))
(is (not (pattern-variable? :?x)))
(is (not (pattern-variable? "?x")))
(is (not (pattern-variable? ['?x])))
(is (not (pattern-variable? '?))))
(defn- segment-pattern?
"Is x a pattern variable representing a segment match?"
(and (symbol? x)
(.startsWith (name x) "?*")
(> (.length (name x)) 2)))
(deftest test-segment-pattern?
(is (not (segment-pattern? '?x)))
(is (not (segment-pattern? '?1)))
(is (not (segment-pattern? '?xy)))
(is (not (segment-pattern? '?1-2)))
(is (segment-pattern? '?*x))
(is (segment-pattern? '?*1))
(is (segment-pattern? '?*xy))
(is (segment-pattern? '?*1-2))
(is (not (segment-pattern? '*)))
(is (not (segment-pattern? 'x?*)))
(is (not (segment-pattern? 'x*?)))
(is (not (segment-pattern? '(?*x))))
(is (not (segment-pattern? :?*x)))
(is (not (segment-pattern? "?*x")))
(is (not (segment-pattern? ['?*x])))
(is (not (segment-pattern? '?*)))
(is (not (segment-pattern? '?))))
(defn- segment-pattern-variable
"Retrieves the variable corresponding to a segment pattern."
{:pre [(.startsWith (name p) "?*")]}
(symbol (str "?" (subs (name p) 2))))
(deftest test-segment-pattern-variable
(is (= '?x (segment-pattern-variable '?*x)))
(is (= '?foo (segment-pattern-variable '?*foo)))
(is (= '?+= (segment-pattern-variable '?*+=))))
(defn- match-pattern-variable
"Does var match input? Uses or updates bindings, then returns them."
[var input bindings]
(let [binding (bindings var)]
(cond (nil? binding) (assoc bindings var input)
(= input binding) bindings
:else nil)))
(defn- match-pattern)
(defn- match-pattern-segment
"Match the segment pattern (?*var pat) against input."
[pattern input bindings]
{:pre [(segment-pattern? (first pattern))]}
(let [var (segment-pattern-variable (first pattern))
pat (rest pattern)]
(if (empty? pat)
(match-pattern-variable var input bindings)
(loop [ps (seq-utils/positions #(= % (first pat)) input)]
(if (empty? ps)
(let [p (first ps)
b2 (match-pattern pat (nthnext input p)
var (take p input) bindings))]
(if (nil? b2) (recur (rest ps)) b2)))))))
(defn- match-pattern
"Match pattern against input in the context of the bindings"
([pattern input bindings]
(cond (empty? pattern) (if (empty? input) bindings nil)
(= (first pattern) (first input))
(match-pattern (rest pattern) (rest input) bindings)
(segment-pattern? (first pattern))
(match-pattern-segment pattern input bindings)
(pattern-variable? (first pattern))
(match-pattern (rest pattern) (rest input)
(match-pattern-variable (first pattern)
(first input)
:else nil))
([pattern input]
(match-pattern pattern input {})))
(defn- rule-pattern [rule] (first rule))
(defn- rule-responses [rule] (rest rule))
(def ^{:private true}
*viewpoint-map* {'I 'you 'you 'I 'me 'you 'am 'are})
(defn- switch-viewpoint
"Change I to you and vice versa, and so on."
(reduce (fn [m pair]
(assoc m (first pair)
(map #(*viewpoint-map* % %) (second pair))))
{} bindings))
(defn use-eliza-rules
"Find some rule with which to transform the input."
(some #(let [result (match-pattern (rule-pattern %) input)]
(when result
(replace (switch-viewpoint result)
(rand-nth (rule-responses %)))))
(defn eliza
"Respond to user input using pattern matching rules."
(print "eliza> ")
(println (flatten (use-eliza-rules (read))))