ruby/step4_if_fn_do.rb

   1 $: << File.expand_path(File.dirname(__FILE__))
   2 require "mal_readline"
   3 require "types"
   4 require "reader"
   5 require "printer"
   6 require "env"
   7 require "core"
   8
   9 # read
  10 def READ(str)
  11     return read_str(str)
  12 end
  13
  14 # eval
  15 def eval_ast(ast, env)
  16     return case ast
  17         when Symbol
  18             env.get(ast)
  19         when List
  20             List.new ast.map{|a| EVAL(a, env)}
  21         when Vector
  22             Vector.new ast.map{|a| EVAL(a, env)}
  23         when Hash
  24             new_hm = {}
  25             ast.each{|k,v| new_hm[EVAL(k,env)] = EVAL(v, env)}
  26             new_hm
  27         else
  28             ast
  29     end
  30 end
  31
  32 def EVAL(ast, env)
  33     #puts "EVAL: #{_pr_str(ast, true)}"
  34
  35     if not ast.is_a? List
  36         return eval_ast(ast, env)
  37     end
  38
  39     # apply list
  40     a0,a1,a2,a3 = ast
  41     case a0
  42     when :def!
  43         return env.set(a1, EVAL(a2, env))
  44     when :"let*"
  45         let_env = Env.new(env)
  46         a1.each_slice(2) do |a,e|
  47             let_env.set(a, EVAL(e, let_env))
  48         end
  49         return EVAL(a2, let_env)
  50     when :do
  51         el = eval_ast(ast.drop(1), env)
  52         return el.last
  53     when :if
  54         cond = EVAL(a1, env)
  55         if not cond
  56             return nil if a3 == nil
  57             return EVAL(a3, env)
  58         else
  59             return EVAL(a2, env)
  60         end
  61     when :"fn*"
  62         return lambda {|*args|
  63             EVAL(a2, Env.new(env, a1, args))
  64         }
  65     else
  66         el = eval_ast(ast, env)
  67         f = el[0]
  68         return f[*el.drop(1)]
  69     end
  70 end
  71
  72 # print
  73 def PRINT(exp)
  74     return _pr_str(exp, true)
  75 end
  76
  77 # repl
  78 repl_env = Env.new
  79 RE = lambda {|str| EVAL(READ(str), repl_env) }
  80 REP = lambda {|str| PRINT(EVAL(READ(str), repl_env)) }
  81
  82 # core.rb: defined using ruby
  83 $core_ns.each do |k,v| repl_env.set(k,v) end
  84
  85 # core.mal: defined using the language itself
  86 RE["(def! not (fn* (a) (if a false true)))"]
  87
  88 # repl loop
  89 while line = _readline("user> ")
  90     begin
  91         puts REP[line]
  92     rescue Exception => e
  93         puts "Error: #{e}"
  94         puts "\t#{e.backtrace.join("\n\t")}"
  95     end
  96 end