lua/step5_tco.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 core = require('core')
  12 local List, Vector, HashMap = types.List, types.Vector, types.HashMap
  13
  14 -- read
  15 function READ(str)
  16     return reader.read_str(str)
  17 end
  18
  19 -- eval
  20 function eval_ast(ast, env)
  21     if types._symbol_Q(ast) then
  22         return env:get(ast)
  23     elseif types._list_Q(ast) then
  24         return List:new(utils.map(function(x) return EVAL(x,env) end,ast))
  25     elseif types._vector_Q(ast) then
  26         return Vector:new(utils.map(function(x) return EVAL(x,env) end,ast))
  27     elseif types._hash_map_Q(ast) then
  28         local new_hm = {}
  29         for k,v in pairs(ast) do
  30             new_hm[EVAL(k, env)] = EVAL(v, env)
  31         end
  32         return HashMap:new(new_hm)
  33     else
  34         return ast
  35     end
  36 end
  37
  38 function EVAL(ast, env)
  39   while true do
  40     --print("EVAL: "..printer._pr_str(ast,true))
  41     if not types._list_Q(ast) then return eval_ast(ast, env) end
  42
  43     local a0,a1,a2,a3 = ast[1], ast[2],ast[3],ast[4]
  44     local a0sym = types._symbol_Q(a0) and a0.val or ""
  45     if 'def!' == a0sym then
  46         return env:set(a1, EVAL(a2, env))
  47     elseif 'let*' == a0sym then
  48         local let_env = Env:new(env)
  49         for i = 1,#a1,2 do
  50             let_env:set(a1[i], EVAL(a1[i+1], let_env))
  51         end
  52         env = let_env
  53         ast = a2 -- TCO
  54     elseif 'do' == a0sym then
  55         local el = eval_ast(ast:slice(2,#ast-1), env)
  56         ast = ast[#ast]  -- TCO
  57     elseif 'if' == a0sym then
  58         local cond = EVAL(a1, env)
  59         if cond == types.Nil or cond == false then
  60             if a3 then ast = a3 else return types.Nil end -- TCO
  61         else
  62             ast = a2 -- TCO
  63         end
  64     elseif 'fn*' == a0sym then
  65         return types.MalFunc:new(function(...)
  66             return EVAL(a2, Env:new(env, a1, arg))
  67         end, a2, env, a1)
  68     else
  69         local args = eval_ast(ast, env)
  70         local f = table.remove(args, 1)
  71         if types._malfunc_Q(f) then
  72             ast = f.ast
  73             env = Env:new(f.env, f.params, args) -- TCO
  74         else
  75             return f(unpack(args))
  76         end
  77     end
  78   end
  79 end
  80
  81 -- print
  82 function PRINT(exp)
  83     return printer._pr_str(exp, true)
  84 end
  85
  86 -- repl
  87 local repl_env = Env:new()
  88 function rep(str)
  89     return PRINT(EVAL(READ(str),repl_env))
  90 end
  91
  92 -- core.lua: defined using Lua
  93 for k,v in pairs(core.ns) do
  94     repl_env:set(types.Symbol:new(k), v)
  95 end
  96
  97 -- core.mal: defined using mal
  98 rep("(def! not (fn* (a) (if a false true)))")
  99
 100 while true do
 101     line = readline.readline("user> ")
 102     if not line then break end
 103     xpcall(function()
 104         print(rep(line))
 105     end, function(exc)
 106         if exc then
 107             if types._malexception_Q(exc) then
 108                 exc = printer._pr_str(exc.val, true)
 109             end
 110             print("Error: " .. exc)
 111             print(debug.traceback())
 112         end
 113     end)
 114 end