Created
September 17, 2016 08:06
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;see http://www.yinwang.org/blog-cn/2012/08/01/interpreter | |
; Clojure 实现的一个简单解释器,是dynamic scope 的 | |
(def env0 {}) | |
(defn ext-env [x v env] | |
(assoc env x v)) | |
(defn lookup | |
"" | |
[x env] | |
(env x)) | |
(def env0 {}) | |
;; 解释器的递归定义(接受两个参数,表达式 exp 和环境 env) | |
;; 共 5 中情况 | |
(defn myeval | |
[exp env] | |
(println (str "debug: " exp " ,env: " env)) | |
(cond | |
(symbol? exp) (let [v (env exp)] | |
(cond | |
v v | |
:else (throw (Throwable. (str "variable undefined" exp))))) ;变量 | |
(number? exp) exp | |
(= (first exp) 'lambda) exp | |
(list? (first exp)) (let [[_ [x] body] (myeval (first exp) env0) | |
v (myeval (second exp) env0) | |
] | |
(myeval body (ext-env x v env0))) | |
:else (let [[op exp1 exp2] exp ;算数表达式 | |
v1 o(myeval exp1 env | |
) | |
v2 (myeval exp2 env | |
)] | |
(cond | |
(= op '+) (+ v1 v2) | |
(= op '-) (- v1 v2) | |
(= op '*) (* v1 v2) | |
(= op '/) (/ v1 v2) | |
)))) |
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