nim/step4_if_fn_do.nim

   1 import rdstdin, tables, sequtils, types, reader, printer, env, core
   2
   3 proc read(str: string): MalType = str.read_str
   4
   5 proc eval(ast: MalType, env: var Env): MalType
   6
   7 proc eval_ast(ast: MalType, env: var Env): MalType =
   8   case ast.kind
   9   of Symbol:
  10     result = env.get(ast.str)
  11   of List:
  12     result = list ast.list.mapIt(MalType, it.eval(env))
  13   of Vector:
  14     result = vector ast.list.mapIt(MalType, it.eval(env))
  15   of HashMap:
  16     result = hash_map()
  17     for k, v in ast.hash_map.pairs:
  18       result.hash_map[k] = v.eval(env)
  19   else:
  20     result = ast
  21
  22 proc eval(ast: MalType, env: var Env): MalType =
  23   case ast.kind
  24   of List:
  25     if ast.list.len == 0: return ast
  26     let a0 = ast.list[0]
  27     case a0.kind
  28     of Symbol:
  29       case a0.str
  30       of "def!":
  31         let
  32           a1 = ast.list[1]
  33           a2 = ast.list[2]
  34         result = env.set(a1.str, a2.eval(env))
  35
  36       of "let*":
  37         let
  38           a1 = ast.list[1]
  39           a2 = ast.list[2]
  40         var letEnv: Env
  41         letEnv.deepCopy(env)
  42
  43         case a1.kind
  44         of List, Vector:
  45           for i in countup(0, a1.list.high, 2):
  46             letEnv.set(a1.list[i].str, a1.list[i+1].eval(letEnv))
  47         else: discard
  48         result = a2.eval(letEnv)
  49
  50       of "do":
  51         let el = (list ast.list[1 .. ^1]).eval_ast(env)
  52         result = el.list[el.list.high]
  53
  54       of "if":
  55         let
  56           a1 = ast.list[1]
  57           a2 = ast.list[2]
  58           cond = a1.eval(env)
  59
  60         if cond.kind in {Nil, False}:
  61           if ast.list.len > 3: result = ast.list[3].eval(env)
  62           else: result = nilObj
  63         else: result = a2.eval(env)
  64
  65       of "fn*":
  66         let
  67           a1 = ast.list[1]
  68           a2 = ast.list[2]
  69         var env2 = env
  70         result = fun(proc(a: varargs[MalType]): MalType =
  71           var newEnv = initEnv(env2, a1, list(a))
  72           a2.eval(newEnv))
  73
  74       else:
  75         let el = ast.eval_ast(env)
  76         result = el.list[0].fun(el.list[1 .. ^1])
  77
  78     else:
  79       let el = ast.eval_ast(env)
  80       result = el.list[0].fun(el.list[1 .. ^1])
  81
  82   else:
  83     result = ast.eval_ast(env)
  84
  85 proc print(exp: MalType): string = exp.pr_str
  86
  87 var repl_env = initEnv()
  88
  89 for k, v in ns.items:
  90   repl_env.set(k, v)
  91
  92 # core.nim: defined using nim
  93 proc rep(str: string): string =
  94   str.read.eval(repl_env).print
  95
  96 # core.mal: defined using mal itself
  97 discard rep "(def! not (fn* (a) (if a false true)))"
  98
  99 while true:
 100   try:
 101     let line = readLineFromStdin("user> ")
 102     echo line.rep
 103   except:
 104     echo getCurrentExceptionMsg()
 105     echo getCurrentException().getStackTrace()