ruby/step5_tco.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 eval_ast(ast, env)
  15     return case ast
  16         when Symbol
  17             env.get(ast)
  18         when List
  19             List.new ast.map{|a| EVAL(a, env)}
  20         when Vector
  21             Vector.new ast.map{|a| EVAL(a, env)}
  22         when Hash
  23             new_hm = {}
  24             ast.each{|k,v| new_hm[EVAL(k,env)] = EVAL(v, env)}
  25             new_hm
  26         else
  27             ast
  28     end
  29 end
  30
  31 def EVAL(ast, env)
  32     while true
  33
  34     #puts "EVAL: #{_pr_str(ast, true)}"
  35
  36     if not ast.is_a? List
  37         return eval_ast(ast, env)
  38     end
  39
  40     # apply list
  41     a0,a1,a2,a3 = ast
  42     case a0
  43     when :def!
  44         return env.set(a1, EVAL(a2, env))
  45     when :"let*"
  46         let_env = Env.new(env)
  47         a1.each_slice(2) do |a,e|
  48             let_env.set(a, EVAL(e, let_env))
  49         end
  50         env = let_env
  51         ast = a2 # Continue loop (TCO)
  52     when :do
  53         eval_ast(ast[1..-2], env)
  54         ast = ast.last # Continue loop (TCO)
  55     when :if
  56         cond = EVAL(a1, env)
  57         if not cond
  58             return nil if a3 == nil
  59             ast = a3 # Continue loop (TCO)
  60         else
  61             ast = a2 # Continue loop (TCO)
  62         end
  63     when :"fn*"
  64         return Function.new(a2, env, a1) {|*args|
  65             EVAL(a2, Env.new(env, a1, args))
  66         }
  67     else
  68         el = eval_ast(ast, env)
  69         f = el[0]
  70         if f.class == Function
  71             ast = f.ast
  72             env = f.gen_env(el.drop(1)) # Continue loop (TCO)
  73         else
  74             return f[*el.drop(1)]
  75         end
  76     end
  77
  78     end
  79 end
  80
  81 # print
  82 def PRINT(exp)
  83     return _pr_str(exp, true)
  84 end
  85
  86 # repl
  87 repl_env = Env.new
  88 RE = lambda {|str| EVAL(READ(str), repl_env) }
  89 REP = lambda {|str| PRINT(EVAL(READ(str), repl_env)) }
  90
  91 # core.rb: defined using ruby
  92 $core_ns.each do |k,v| repl_env.set(k,v) end
  93
  94 # core.mal: defined using the language itself
  95 RE["(def! not (fn* (a) (if a false true)))"]
  96
  97 # repl loop
  98 while line = _readline("user> ")
  99     begin
 100         puts REP[line]
 101     rescue Exception => e
 102         puts "Error: #{e}"
 103         puts "\t#{e.backtrace.join("\n\t")}"
 104     end
 105 end