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(ns lccl.lc.evaluator
(:import [lccl.lc.ast Var Abs App])
(:require [lccl.lc.ast :refer [->Abs ->App]]))
(declare substitute)
(defmulti evaluate (fn [term] [(type term)]))
(defmethod evaluate [Var] ([term] term))
(defmethod evaluate [Abs] ([term] term))
(defmethod evaluate [App]
([term]
(let [left (-> term :left)]
(condp = (type left)
Abs (substitute (:body left) (:arg left) (:right term))
term))))
(defmulti substitute (fn [body arg val] [(type body)]))
(defmethod substitute [Var]
([body arg val]
(if (= (:name body) arg) val body)))
(defmethod substitute [Abs]
([body arg val]
(if (= (:arg body) arg)
body
(->Abs (:arg body) (substitute (:body body) arg val)))))
(defmethod substitute [App]
([body arg val]
(->App (substitute (:left body) arg val) (substitute (:right body) arg val))))
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