step8_macros.hy

#!/usr/bin/env hy

(import [hy.models [HyString :as Str HySymbol :as Sym]])
(import sys traceback)
(import [reader [read-str Blank]])
(import [printer [pr-str]])
(import [env [env-new env-get env-set env-find]])
(import core)

;; read
(defn READ [str]
  (read-str str))

;; eval
(defn pair? [x]
  (and (core.sequential? x) (> (len x) 0)))

(defn QUASIQUOTE [ast]
  (if
    (not (pair? ast))
    (tuple [(Sym "quote") ast])

    (= (Sym "unquote") (first ast))
    (nth ast 1)

    (and (pair? (first ast))
         (= (Sym "splice-unquote") (first (first ast))))
    (tuple [(Sym "concat") (nth (first ast) 1) (QUASIQUOTE (tuple (rest ast)))])

    True
    (tuple [(Sym "cons") (QUASIQUOTE (first ast)) (QUASIQUOTE (tuple (rest ast)))])))

(defn macro? [ast env]
  (when (and (coll? ast)
             (symbol? (first ast))
             (env-find env (first ast)))
    (setv mac (env-get env (first ast)))
    (and (hasattr mac "macro")
         mac.macro)))

(defn macroexpand [ast env]
 (while (macro? ast env)
   (setv mac (env-get env (first ast))
         ast (apply mac (tuple (rest ast)))))
 ast)



(defn eval-ast [ast env]
  ;;(print "eval-ast:" ast (type ast))
  (if
    (symbol? ast)         (env-get env ast)
    (instance? dict ast)  (dict (map (fn [k]
                                       [(EVAL k env) (EVAL (get ast k) env)])
                                     ast))
    (instance? tuple ast) (tuple (map (fn [x] (EVAL x env)) ast))
    (instance? list ast)  (list (map (fn [x] (EVAL x env)) ast))
    True                  ast))

(defn EVAL [ast env]
  ;;(print "EVAL:" ast (type ast) (instance? tuple ast))
  (setv res None)
  (while True
    (setv res
      (if (not (instance? tuple ast))
        (eval-ast ast env)

        ;; apply list
        (do
          (setv ast (macroexpand ast env))
          (if (not (instance? tuple ast))
            (eval-ast ast env)

            (do
              (setv [a0 a1 a2] [(nth ast 0) (nth ast 1) (nth ast 2)])
              (if
                (none? a0)
                ast

                (= (Sym "def!") a0)
                (env-set env a1 (EVAL a2 env))

                (= (Sym "let*") a0)
                (do
                  (setv env (env-new env))
                  (for [[b e] (partition a1 2)]
                    (env-set env b (EVAL e env)))
                  (setv ast a2)
                  (continue)) ;; TCO

                (= (Sym "quote") a0)
                a1

                (= (Sym "quasiquote") a0)
                (do (setv ast (QUASIQUOTE a1)) (continue)) ;; TCO

                (= (Sym "defmacro!") a0)
                (do (setv func (EVAL a2 env)
                          func.macro True)
                    (env-set env a1 func))

                (= (Sym "macroexpand") a0)
                (macroexpand a1 env)

                (= (Sym "do") a0)
                (do (eval-ast (list (butlast (rest ast))) env)
                    (setv ast (last ast))
                    (continue)) ;; TCO

                (= (Sym "if") a0)
                (do
                  (setv cond (EVAL a1 env))
                  (if (or (none? cond) (and (instance? bool cond)
                                            (= cond False)))
                    (if (> (len ast) 2)
                      (do (setv ast (nth ast 3)) (continue)) ;; TCO
                      None)
                    (do (setv ast a2) (continue)))) ;; TCO

                (= (Sym "fn*") a0)
                (do
                  (setv func (fn [&rest args]
                               (EVAL a2 (env-new env a1 (or args []))))
                        func.ast a2
                        func.env env
                        func.params a1)
                  func)

                ;; apply
                (do
                  (setv el (eval-ast ast env)
                        f (first el)
                        args (list (rest el)))
                  (if (hasattr f "ast")
                    (do (setv ast f.ast
                              env (env-new f.env f.params args))
                        (continue)) ;; TCO
                    (apply f args)))))))))
    (break))
  res)

;; print
(defn PRINT [exp]
  (pr-str exp True))

;; repl
(def repl-env (env-new))
(defn REP [str]
  (PRINT (EVAL (READ str) repl-env)))

;; core.hy: defined using Hy
(for [k core.ns]
  (env-set repl-env (Sym k) (get core.ns k)))
(env-set repl-env (Sym "eval") (fn [ast] (EVAL ast repl-env)))
(env-set repl-env (Sym "*ARGV*") (, ))

;; core.mal: defined using the language itself
(REP "(def! not (fn* [a] (if a false true)))")
(REP "(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \")\")))))")
(REP "(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list 'if (first xs) (if (> (count xs) 1) (nth xs 1) (throw \"odd number of forms to cond\")) (cons 'cond (rest (rest xs)))))))")
(REP "(defmacro! or (fn* (& xs) (if (empty? xs) nil (if (= 1 (count xs)) (first xs) `(let* (or_FIXME ~(first xs)) (if or_FIXME or_FIXME (or ~@(rest xs))))))))")

(defmain [&rest args]
  (if (>= (len args) 2)
    (do
      (env-set repl-env (Sym "*ARGV*") (tuple (map Str (rest (rest args)))))
      (REP (+ "(load-file \"" (get args 1) "\")")))
    (do
      (while True
        (try
          (do (setv line (raw_input "user> "))
              (if (= "" line) (continue))
              (print (REP line)))
          (except [EOFError] (break))
          (except [Blank])
          (except []
            (print (.join "" (apply traceback.format_exception
                                    (.exc_info sys))))))))))