lua/step3_env.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 Env = require('env')
  11 local List, Vector, HashMap = types.List, types.Vector, types.HashMap
  12
  13 -- read
  14 function READ(str)
  15     return reader.read_str(str)
  16 end
  17
  18 -- eval
  19 function eval_ast(ast, env)
  20     if types._symbol_Q(ast) then
  21         return env:get(ast)
  22     elseif types._list_Q(ast) then
  23         return List:new(utils.map(function(x) return EVAL(x,env) end,ast))
  24     elseif types._vector_Q(ast) then
  25         return Vector:new(utils.map(function(x) return EVAL(x,env) end,ast))
  26     elseif types._hash_map_Q(ast) then
  27         local new_hm = {}
  28         for k,v in pairs(ast) do
  29             new_hm[EVAL(k, env)] = EVAL(v, env)
  30         end
  31         return HashMap:new(new_hm)
  32     else
  33         return ast
  34     end
  35 end
  36
  37 function EVAL(ast, env)
  38     --print("EVAL: "..printer._pr_str(ast,true))
  39     if not types._list_Q(ast) then return eval_ast(ast, env) end
  40
  41     local a0,a1,a2 = ast[1], ast[2],ast[3]
  42     local a0sym = types._symbol_Q(a0) and a0.val or ""
  43     if 'def!' == a0sym then
  44         return env:set(a1, EVAL(a2, env))
  45     elseif 'let*' == a0sym then
  46         local let_env = Env:new(env)
  47         for i = 1,#a1,2 do
  48             let_env:set(a1[i], EVAL(a1[i+1], let_env))
  49         end
  50         return EVAL(a2, let_env)
  51     else
  52         local args = eval_ast(ast, env)
  53         local f = table.remove(args, 1)
  54         return f(unpack(args))
  55     end
  56 end
  57
  58 -- print
  59 function PRINT(exp)
  60     return printer._pr_str(exp, true)
  61 end
  62
  63 -- repl
  64 local repl_env = Env:new()
  65 function rep(str)
  66     return PRINT(EVAL(READ(str),repl_env))
  67 end
  68
  69 repl_env:set(types.Symbol:new('+'), function(a,b) return a+b end)
  70 repl_env:set(types.Symbol:new('-'), function(a,b) return a-b end)
  71 repl_env:set(types.Symbol:new('*'), function(a,b) return a*b end)
  72 repl_env:set(types.Symbol:new('/'), function(a,b) return math.floor(a/b) end)
  73
  74 while true do
  75     line = readline.readline("user> ")
  76     if not line then break end
  77     xpcall(function()
  78         print(rep(line))
  79     end, function(exc)
  80         if exc then
  81             if types._malexception_Q(exc) then
  82                 exc = printer._pr_str(exc.val, true)
  83             end
  84             print("Error: " .. exc)
  85             print(debug.traceback())
  86         end
  87     end)
  88 end