scala/step2_eval.scala

   1 import types.{MalList, _list_Q, MalVector, MalHashMap, MalFunction}
   2
   3 object step2_eval {
   4   // read
   5   def READ(str: String): Any = {
   6     reader.read_str(str)
   7   }
   8
   9   // eval
  10   def eval_ast(ast: Any, env: Map[Symbol,Any]): Any = {
  11     ast match {
  12       case s : Symbol    => env(s)
  13       case v: MalVector  => v.map(EVAL(_, env))
  14       case l: MalList    => l.map(EVAL(_, env))
  15       case m: MalHashMap => {
  16         m.map{case (k,v) => (k, EVAL(v, env))}
  17       }
  18       case _             => ast
  19     }
  20   }
  21
  22   def EVAL(ast: Any, env: Map[Symbol,Any]): Any = {
  23     //println("EVAL: " + printer._pr_str(ast,true))
  24     if (!_list_Q(ast))
  25       return eval_ast(ast, env)
  26
  27     // apply list
  28     if (ast.asInstanceOf[MalList].value.length == 0)
  29       return ast
  30     eval_ast(ast, env).asInstanceOf[MalList].value match {
  31       case f :: el => {
  32         var fn: List[Any] => Any = null
  33         try {
  34           fn = f.asInstanceOf[List[Any] => Any]
  35         } catch {
  36           case _: Throwable =>
  37             throw new Exception("attempt to call non-function")
  38         }
  39         return fn(el)
  40       }
  41       case _ => throw new Exception("invalid apply")
  42     }
  43   }
  44
  45   // print
  46   def PRINT(exp: Any): String = {
  47     printer._pr_str(exp, true)
  48   }
  49
  50   // repl
  51   def main(args: Array[String]) = {
  52     val repl_env: Map[Symbol,Any] = Map(
  53       '+ -> ((a: List[Any]) => a(0).asInstanceOf[Long] + a(1).asInstanceOf[Long]),
  54       '- -> ((a: List[Any]) => a(0).asInstanceOf[Long] - a(1).asInstanceOf[Long]),
  55       '* -> ((a: List[Any]) => a(0).asInstanceOf[Long] * a(1).asInstanceOf[Long]),
  56       '/ -> ((a: List[Any]) => a(0).asInstanceOf[Long] / a(1).asInstanceOf[Long]))
  57     val REP = (str: String) => {
  58       PRINT(EVAL(READ(str), repl_env))
  59     }
  60
  61     var line:String = null
  62     while ({line = readLine("user> "); line != null}) {
  63       try {
  64         println(REP(line))
  65       } catch {
  66         case e : Exception => {
  67           println("Error: " + e.getMessage)
  68           println("    " + e.getStackTrace.mkString("\n    "))
  69         }
  70       }
  71     }
  72   }
  73 }
  74
  75 // vim: ts=2:sw=2