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