Re: Postfix notation with a binary Tree

["Robert I. Eachus" <rieachus@comcast.net>]

tchou wrote:

> Hello everyone,
> 
> Which type should I use to do a binary tree for calculation, using a
> postfix notation?
> 
> '+' '-' -> character
> 6876, 23.42, 1 -> Integer OR string
> 
> Is a conversion to string the only / best solution?

No, you can use either tagged types or variant records to create a 
heterogenous data structure.  For this application I prefer variant records:

type Content_Type is (Operator, Integer_Value, Float_Value, ...);

type Node;

type Node_Pointer is access all Node;

type Node(Content: Content_Type) is record
   Left, Right: Node_Pointer;
   case Content_Type is
     when Operator => Op: Character;
     when Integer_Value => Int: Integer;
     ...
   end case;
end record;

-- 

                                           Robert I. Eachus

"The terrorist enemy holds no territory, defends no population, is 
unconstrained by rules of warfare, and respects no law of morality. Such 
an enemy cannot be deterred, contained, appeased or negotiated with. It 
can only be destroyed--and that, ladies and gentlemen, is the business 
at hand."  -- Dick Cheney