ruby/step8_macros.rb

   1 require_relative "mal_readline"
   2 require_relative "types"
   3 require_relative "reader"
   4 require_relative "printer"
   5 require_relative "env"
   6 require_relative "core"
   7
   8 # read
   9 def READ(str)
  10     return read_str(str)
  11 end
  12
  13 # eval
  14 def pair?(x)
  15     return sequential?(x) && x.size > 0
  16 end
  17
  18 def quasiquote(ast)
  19     if not pair?(ast)
  20         return List.new [:quote, ast]
  21     elsif ast[0] == :unquote
  22         return ast[1]
  23     elsif pair?(ast[0]) && ast[0][0] == :"splice-unquote"
  24         return List.new [:concat, ast[0][1], quasiquote(ast.drop(1))]
  25     else
  26         return List.new [:cons, quasiquote(ast[0]), quasiquote(ast.drop(1))]
  27     end
  28 end
  29
  30 def macro_call?(ast, env)
  31     return (ast.is_a?(List) &&
  32             ast[0].is_a?(Symbol) &&
  33             env.find(ast[0]) &&
  34             env.get(ast[0]).is_a?(Function) &&
  35             env.get(ast[0]).is_macro)
  36 end
  37
  38 def macroexpand(ast, env)
  39     while macro_call?(ast, env)
  40         mac = env.get(ast[0])
  41         ast = mac[*ast.drop(1)]
  42     end
  43     return ast
  44 end
  45
  46 def eval_ast(ast, env)
  47     return case ast
  48         when Symbol
  49             env.get(ast)
  50         when List
  51             List.new ast.map{|a| EVAL(a, env)}
  52         when Vector
  53             Vector.new ast.map{|a| EVAL(a, env)}
  54         when Hash
  55             new_hm = {}
  56             ast.each{|k,v| new_hm[EVAL(k,env)] = EVAL(v, env)}
  57             new_hm
  58         else
  59             ast
  60     end
  61 end
  62
  63 def EVAL(ast, env)
  64     while true
  65
  66     #puts "EVAL: #{_pr_str(ast, true)}"
  67
  68     if not ast.is_a? List
  69         return eval_ast(ast, env)
  70     end
  71
  72     # apply list
  73     ast = macroexpand(ast, env)
  74     if not ast.is_a? List
  75         return eval_ast(ast, env)
  76     end
  77     if ast.empty?
  78         return ast
  79     end
  80
  81     a0,a1,a2,a3 = ast
  82     case a0
  83     when :def!
  84         return env.set(a1, EVAL(a2, env))
  85     when :"let*"
  86         let_env = Env.new(env)
  87         a1.each_slice(2) do |a,e|
  88             let_env.set(a, EVAL(e, let_env))
  89         end
  90         env = let_env
  91         ast = a2 # Continue loop (TCO)
  92     when :quote
  93         return a1
  94     when :quasiquote
  95         ast = quasiquote(a1); # Continue loop (TCO)
  96     when :defmacro!
  97         func = EVAL(a2, env)
  98         func.is_macro = true
  99         return env.set(a1, func)
 100     when :macroexpand
 101         return macroexpand(a1, env)
 102     when :do
 103         eval_ast(ast[1..-2], env)
 104         ast = ast.last # Continue loop (TCO)
 105     when :if
 106         cond = EVAL(a1, env)
 107         if not cond
 108             return nil if a3 == nil
 109             ast = a3 # Continue loop (TCO)
 110         else
 111             ast = a2 # Continue loop (TCO)
 112         end
 113     when :"fn*"
 114         return Function.new(a2, env, a1) {|*args|
 115             EVAL(a2, Env.new(env, a1, List.new(args)))
 116         }
 117     else
 118         el = eval_ast(ast, env)
 119         f = el[0]
 120         if f.class == Function
 121             ast = f.ast
 122             env = f.gen_env(el.drop(1)) # Continue loop (TCO)
 123         else
 124             return f[*el.drop(1)]
 125         end
 126     end
 127
 128     end
 129 end
 130
 131 # print
 132 def PRINT(exp)
 133     return _pr_str(exp, true)
 134 end
 135
 136 # repl
 137 repl_env = Env.new
 138 RE = lambda {|str| EVAL(READ(str), repl_env) }
 139 REP = lambda {|str| PRINT(EVAL(READ(str), repl_env)) }
 140
 141 # core.rb: defined using ruby
 142 $core_ns.each do |k,v| repl_env.set(k,v) end
 143 repl_env.set(:eval, lambda {|ast| EVAL(ast, repl_env)})
 144 repl_env.set(:"*ARGV*", List.new(ARGV.slice(1,ARGV.length) || []))
 145
 146 # core.mal: defined using the language itself
 147 RE["(def! not (fn* (a) (if a false true)))"]
 148 RE["(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \")\")))))"]
 149 RE["(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)))))))"]
 150 RE["(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))))))))"]
 151
 152 if ARGV.size > 0
 153     RE["(load-file \"" + ARGV[0] + "\")"]
 154     exit 0
 155 end
 156
 157 # repl loop
 158 while line = _readline("user> ")
 159     begin
 160         puts REP[line]
 161     rescue Exception => e
 162         puts "Error: #{e}"
 163         puts "\t#{e.backtrace.join("\n\t")}"
 164     end
 165 end