lua/step4_if_fn_do.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     --print("EVAL: "..printer._pr_str(ast,true))
  40     if not types._list_Q(ast) then return eval_ast(ast, env) end
  41
  42     local a0,a1,a2,a3 = ast[1], ast[2],ast[3],ast[4]
  43     local a0sym = types._symbol_Q(a0) and a0.val or ""
  44     if 'def!' == a0sym then
  45         return env:set(a1, EVAL(a2, env))
  46     elseif 'let*' == a0sym then
  47         local let_env = Env:new(env)
  48         for i = 1,#a1,2 do
  49             let_env:set(a1[i], EVAL(a1[i+1], let_env))
  50         end
  51         return EVAL(a2, let_env)
  52     elseif 'do' == a0sym then
  53         local el = eval_ast(ast:slice(2,#ast), env)
  54         return el[#el]
  55     elseif 'if' == a0sym then
  56         local cond = EVAL(a1, env)
  57         if cond == types.Nil or cond == false then
  58             if a3 then return EVAL(a3, env) else return types.Nil end
  59         else
  60             return EVAL(a2, env)
  61         end
  62     elseif 'fn*' == a0sym then
  63         return function(...)
  64             return EVAL(a2, Env:new(env, a1, arg))
  65         end
  66     else
  67         local args = eval_ast(ast, env)
  68         local f = table.remove(args, 1)
  69         return f(unpack(args))
  70     end
  71 end
  72
  73 -- print
  74 function PRINT(exp)
  75     return printer._pr_str(exp, true)
  76 end
  77
  78 -- repl
  79 local repl_env = Env:new()
  80 function rep(str)
  81     return PRINT(EVAL(READ(str),repl_env))
  82 end
  83
  84 -- core.lua: defined using Lua
  85 for k,v in pairs(core.ns) do
  86     repl_env:set(types.Symbol:new(k), v)
  87 end
  88
  89 -- core.mal: defined using mal
  90 rep("(def! not (fn* (a) (if a false true)))")
  91
  92 while true do
  93     line = readline.readline("user> ")
  94     if not line then break end
  95     xpcall(function()
  96         print(rep(line))
  97     end, function(exc)
  98         if exc then
  99             if types._malexception_Q(exc) then
 100                 exc = printer._pr_str(exc.val, true)
 101             end
 102             print("Error: " .. exc)
 103             print(debug.traceback())
 104         end
 105     end)
 106 end