Re: S-expression I/O in Ada

[Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>]

On 08/01/2010 05:17 AM, Natacha Kerensikova wrote:
>
> To describe briefly S-expressions, I consider them to be the simplest
> existing data organization beyond raw sequences of bits. They are
> basically lists of elements, each element being either a list or an
> atom, and atoms being raw sequences of bits.

You might very well be able to use something like:

package Byte_Lists is new Ada.Containers.Vectors (Index_Type => Positive, 
Element_Type => System.Storage_Elements.Storage_Element);

type Content_ID is (Atom, List);

type S_Expression;
type S_Expression_Ptr is access all S_Expression;

type S_Expression_Element (Content : Content_ID := Atom) is record
    case Content is
    when Atom =>
       Byte : Byte_Lists.Vector;
    when List =>
       Ptr : S_Expression_Ptr;
    end case;
end record;

package S_Expression_Lists is new Ada.Containers.Doubly_Linked_Lists 
(Element_Type => S_Expression_Element);

type S_Expression is new S_Expression_Lists.List;

If you can use unbounded strings as Brenta suggested, instead of an unbounded 
array of bytes (Storage_Element), then this would be even simpler.

-- 
Jeff Carter
"People called Romanes, they go the house?"
Monty Python's Life of Brian
79

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