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     if #ast == 0 then return ast end
  43     local args = eval_ast(ast, env)
  44     local f = table.remove(args, 1)
  45     return f(unpack(args))
  46 end
  47
  48 -- print
  49 function PRINT(exp)
  50     return printer._pr_str(exp, true)
  51 end
  52
  53 -- repl
  54 local repl_env = {['+'] = function(a,b) return a+b end,
  55                   ['-'] = function(a,b) return a-b end,
  56                   ['*'] = function(a,b) return a*b end,
  57                   ['/'] = function(a,b) return math.floor(a/b) end}
  58 function rep(str)
  59     return PRINT(EVAL(READ(str),repl_env))
  60 end
  61
  62 if #arg > 0 and arg[1] == "--raw" then
  63     readline.raw = true
  64 end
  65
  66 while true do
  67     line = readline.readline("user> ")
  68     if not line then break end
  69     xpcall(function()
  70         print(rep(line))
  71     end, function(exc)
  72         if exc then
  73             if types._malexception_Q(exc) then
  74                 exc = printer._pr_str(exc.val, true)
  75             end
  76             print("Error: " .. exc)
  77             print(debug.traceback())
  78         end
  79     end)
  80 end