private void AddVarToVarTable(string varName, ZOperand zOperand) {
if (varTable.Peek().ContainsKey(varName)) throw new Exception("variable " + varName + " can't have duplicate definition");
varTable.Peek()[varName] = zOperand;
}
private ZOperand Compute(ZOperand left, string oper, ZOperand right = null) {
//very important
Operand resultValue = null;
resultValue = right == null ? Compute(left.Operand, oper, null) : Compute(left.Operand, oper, right.Operand);
if (resultValue == null) throw new Exception("invaild expression");
else {
return new ZOperand(resultValue, getTypeString(resultValue.GetReturnType(tm)));
}
}