clojure/src/step2_eval.clj

   1 (ns step2-eval
   2     (:require [clojure.repl]
   3               [readline]
   4               [reader]
   5               [printer]))
   6
   7 ;; read
   8 (defn READ [& [strng]]
   9   (let [line (if strng strng (read-line))]
  10     (reader/read-string strng)))
  11
  12 ;; eval
  13 (declare EVAL)
  14 (defn eval-ast [ast env]
  15   (cond
  16     (symbol? ast) (or (get env ast)
  17                       (throw (Error. (str ast " not found"))))
  18
  19     (seq? ast)    (doall (map #(EVAL % env) ast))
  20
  21     (vector? ast) (vec (doall (map #(EVAL % env) ast)))
  22
  23     (map? ast)    (apply hash-map (doall (map #(EVAL % env)
  24                                               (mapcat identity ast))))
  25
  26     :else         ast))
  27
  28 (defn EVAL [ast env]
  29   ;;(prn "EVAL" ast (keys @env)) (flush)
  30   (if (not (seq? ast))
  31     (eval-ast ast env)
  32
  33     ;; apply list
  34     (let [el (eval-ast ast env)
  35           f (first el)
  36           args (rest el)]
  37       (apply f args))))
  38
  39 ;; print
  40 (defn PRINT [exp] (pr-str exp))
  41
  42 ;; repl
  43 (def repl-env {'+ +
  44                '- -
  45                '* *
  46                '/ /})
  47 (defn rep
  48   [strng]
  49   (PRINT (EVAL (READ strng) repl-env)))
  50
  51 ;; repl loop
  52 (defn repl-loop []
  53   (let [line (readline/readline "user> ")]
  54     (when line
  55       (when-not (re-seq #"^\s*$|^\s*;.*$" line) ; blank/comment
  56         (try
  57           (println (rep line))
  58           (catch Throwable e
  59             (clojure.repl/pst e))))
  60       (recur))))
  61
  62 (defn -main [& args]
  63   (repl-loop))