const{ var _n=-1; var[proxy]N=fcn{ _n+=1 }; }  // enumerator
const FETCH=N, STORE=N, PUSH=N, ADD=N,  SUB=N,  MUL=N, DIV=N, MOD=N,
      LT=N,    GT=N,    LE=N,   GE=N,   EQ=N,   NE=N,
      AND=N,   OR=N,    NEG=N,  NOT=N,
      JMP=N,   JZ=N,    PRTC=N, PRTS=N, PRTI=N, HALT=N;
const nd_String=N, nd_Sequence=N, nd_If=N, nd_While=N;
var [const]
   all_syms=Dictionary(
      "Identifier"  ,FETCH,       "String"      ,nd_String,
      "Integer"     ,PUSH,        "Sequence"    ,nd_Sequence,
      "If"          ,nd_If,       "Prtc"        ,PRTC,
      "Prts"        ,PRTS,        "Prti"        ,PRTI,
      "While"       ,nd_While,    "Assign"      ,STORE,
      "Negate"      ,NEG,         "Not"         ,NOT,
      "Multiply"    ,MUL,         "Divide"      ,DIV,
      "Mod"         ,MOD,         "Add"         ,ADD,
      "Subtract"    ,SUB,         "Less"        ,LT,
      "LessEqual"   ,LE,          "Greater"     ,GT,
      "GreaterEqual",GE,          "Equal"       ,EQ,
      "NotEqual"    ,NE,          "And"         ,AND,
      "Or"          ,OR,	  "halt"	,HALT),
   bops=Dictionary(ADD,'+, SUB,'-, MUL,'*, DIV,'/, MOD,'%,
		   LT,'<, GT,'>, LE,'<=, GE,'>=, NE,'!=, EQ,'==, NE,'!=);

class Node{
   fcn init(_node_type, _value, _left=Void, _right=Void){
      var type=_node_type, left=_left, right=_right, value=_value;
   }
}

fcn runNode(node){
   var vars=Dictionary();  // fcn local static var
   if(Void==node) return();
   switch(node.type){
      case(PUSH,nd_String){ return(node.value) }
      case(FETCH){ return(vars[node.value]) }
      case(STORE){ vars[node.left.value]=runNode(node.right); return(Void); }
      case(nd_If){
         if(runNode(node.left)) runNode(node.right.left);
	 else                   runNode(node.right.right);
      }
      case(nd_While)
         { while(runNode(node.left)){ runNode(node.right) } return(Void) }
      case(nd_Sequence){ runNode(node.left); runNode(node.right); return(Void) }
      case(PRTC)       { print(runNode(node.left).toAsc()) }
      case(PRTI,PRTS)  { print(runNode(node.left)) }
      case(NEG)        { return(-runNode(node.left)) }
      case(NOT)        { return(not runNode(node.left)) }
      case(AND)        { return(runNode(node.left) and runNode(node.right)) }
      case(OR)         { return(runNode(node.left) or  runNode(node.right)) }
      else{
	 if(op:=bops.find(node.type))
	    return(op(runNode(node.left),runNode(node.right)));
	 else throw(Exception.AssertionError(
	    "Unknown node type: %d".fmt(node.type)))
      }
   }
   Void
}