lua/step2_eval.lua

   1 #!/usr/bin/env lua
   2
   3 local table = require('table')
   4
   5 local readline = require('readline')
   6 local utils = require('utils')
   7 local types = require('types')
   8 local reader = require('reader')
   9 local printer = require('printer')
  10 local List, Vector, HashMap = types.List, types.Vector, types.HashMap
  11
  12 -- read
  13 function READ(str)
  14     return reader.read_str(str)
  15 end
  16
  17 -- eval
  18 function eval_ast(ast, env)
  19     if types._symbol_Q(ast) then
  20         if env[ast.val] == nil then
  21             types.throw("'"..ast.val.."' not found")
  22         end
  23         return env[ast.val]
  24     elseif types._list_Q(ast) then
  25         return List:new(utils.map(function(x) return EVAL(x,env) end,ast))
  26     elseif types._vector_Q(ast) then
  27         return Vector:new(utils.map(function(x) return EVAL(x,env) end,ast))
  28     elseif types._hash_map_Q(ast) then
  29         local new_hm = {}
  30         for k,v in pairs(ast) do
  31             new_hm[EVAL(k, env)] = EVAL(v, env)
  32         end
  33         return HashMap:new(new_hm)
  34     else
  35         return ast
  36     end
  37 end
  38
  39 function EVAL(ast, env)
  40     --print("EVAL: "..printer._pr_str(ast,true))
  41     if not types._list_Q(ast) then return eval_ast(ast, env) end
  42     local args = eval_ast(ast, env)
  43     local f = table.remove(args, 1)
  44     return f(unpack(args))
  45 end
  46
  47 -- print
  48 function PRINT(exp)
  49     return printer._pr_str(exp, true)
  50 end
  51
  52 -- repl
  53 local repl_env = {['+'] = function(a,b) return a+b end,
  54                   ['-'] = function(a,b) return a-b end,
  55                   ['*'] = function(a,b) return a*b end,
  56                   ['/'] = function(a,b) return math.floor(a/b) end}
  57 function rep(str)
  58     return PRINT(EVAL(READ(str),repl_env))
  59 end
  60
  61 if #arg > 0 and arg[1] == "--raw" then
  62     readline.raw = true
  63 end
  64
  65 while true do
  66     line = readline.readline("user> ")
  67     if not line then break end
  68     xpcall(function()
  69         print(rep(line))
  70     end, function(exc)
  71         if exc then
  72             if types._malexception_Q(exc) then
  73                 exc = printer._pr_str(exc.val, true)
  74             end
  75             print("Error: " .. exc)
  76             print(debug.traceback())
  77         end
  78     end)
  79 end