io/step5_tco.io

   1 MalTypes
   2 MalReader
   3
   4 READ := method(str, MalReader read_str(str))
   5
   6 eval_ast := method(ast, env,
   7    (ast type) switch(
   8        "MalSymbol", env get(ast),
   9        "MalList", MalList with(ast map(a, EVAL(a, env))),
  10        "MalVector", MalVector with(ast map(a, EVAL(a, env))),
  11        "MalMap",
  12            m := MalMap clone
  13            ast foreach(k, v,
  14                keyObj := MalMap keyToObj(k)
  15                m atPut(MalMap objToKey(EVAL(keyObj, env)), EVAL(v, env))
  16            )
  17            m,
  18        ast
  19    )
  20 )
  21
  22 EVAL := method(ast, env,
  23     loop(
  24         if(ast type != "MalList", return(eval_ast(ast, env)))
  25         if(ast isEmpty, return ast)
  26         if(ast at(0) type == "MalSymbol",
  27             ast at(0) val switch(
  28                 "def!",
  29                     return(env set(ast at(1), EVAL(ast at(2), env))),
  30                 "do",
  31                     eval_ast(ast slice(1,-1), env)
  32                     ast = ast last
  33                     continue, // TCO
  34                 "if",
  35                     ast = if(EVAL(ast at(1), env), ast at(2), ast at(3))
  36                     continue, // TCO
  37                 "fn*",
  38                     return(MalFunc with(ast at(2), ast at(1), env, block(a, EVAL(ast at(2), Env with(env, ast at(1), a))))),
  39                 "let*",
  40                     letEnv := Env with(env)
  41                     varName := nil
  42                     ast at(1) foreach(i, e,
  43                         if(i % 2 == 0,
  44                             varName := e,
  45                             letEnv set(varName, EVAL(e, letEnv))
  46                         )
  47                     )
  48                     ast = ast at(2)
  49                     env = letEnv
  50                     continue // TCO
  51             )
  52         )
  53
  54         // Apply
  55         el := eval_ast(ast, env)
  56         f := el at(0)
  57         args := el rest
  58         f type switch(
  59             "Block",
  60                 return(f call(args)),
  61             "MalFunc",
  62                 ast = f ast
  63                 env = Env with(f env, f params, args)
  64                 continue, // TCO
  65             Exception raise("Unknown function type")
  66         )
  67     )
  68 )
  69
  70 PRINT := method(exp, exp malPrint(true))
  71
  72 RE := method(str, EVAL(READ(str), repl_env))
  73
  74 REP := method(str, PRINT(RE(str)))
  75
  76 repl_env := Env with(nil)
  77 MalCore NS foreach(k, v, repl_env set(MalSymbol with(k), v))
  78
  79 // core.mal: defined using the language itself
  80 RE("(def! not (fn* (a) (if a false true)))")
  81
  82 loop(
  83     line := MalReadline readLine("user> ")
  84     if(line isNil, break)
  85     if(line isEmpty, continue)
  86     e := try(REP(line) println)
  87     e catch(Exception,
  88         if(e type == "MalException",
  89             ("Error: " .. ((e val) malPrint(true))) println,
  90             ("Error: " .. (e error)) println
  91         )
  92     )
  93 )