hy/step2_eval.hy

   1 #!/usr/bin/env hy
   2
   3 (import sys traceback)
   4 (import [reader [read-str Blank]])
   5 (import [printer [pr-str]])
   6
   7 ;; read
   8 (defn READ [str]
   9   (read-str str))
  10
  11 ;; eval
  12 (defn eval-ast [ast env]
  13   (if
  14     (symbol? ast)         (if (.has_key env ast) (get env ast)
  15                               (raise (Exception (+ ast " not found"))))
  16     (instance? dict ast)  (dict (map (fn [k]
  17                                        [(EVAL k env) (EVAL (get ast k) env)])
  18                                      ast))
  19     (instance? tuple ast) (tuple (map (fn [x] (EVAL x env)) ast))
  20     (instance? list ast)  (list (map (fn [x] (EVAL x env)) ast))
  21     True                  ast))
  22
  23 (defn EVAL [ast env]
  24   ;; indented to match later steps
  25       (if (not (instance? tuple ast))
  26         (eval-ast ast env)
  27
  28         ;; apply list
  29               (if
  30                 (empty? ast)
  31                 ast
  32
  33                 ;; apply
  34                 (do
  35                   (setv el (eval-ast ast env)
  36                         f (first el)
  37                         args (list (rest el)))
  38                   (apply f args)))))
  39
  40 ;; print
  41 (defn PRINT [exp]
  42   (pr-str exp True))
  43
  44 ;; repl
  45 (def repl-env {'+ +
  46                '- -
  47                '* *
  48                '/ (fn [a b] (int (/ a b)))})
  49
  50 (defn REP [str]
  51   (PRINT (EVAL (READ str) repl-env)))
  52
  53 (defmain [&rest args]
  54   ;; indented to match later steps
  55       (while True
  56         (try
  57           (do (setv line (raw_input "user> "))
  58               (if (= "" line) (continue))
  59               (print (REP line)))
  60           (except [EOFError] (break))
  61           (except [Blank])
  62           (except [e Exception]
  63             (print (.join "" (apply traceback.format_exception
  64                                     (.exc_info sys))))))))