Re: HELP : linked lists in ADA

[Vincent Celier <vcelier@direct.ca>]

Richard Clavelier wrote:
> 
>   Hello,

I believe you may be one of these students that posts to the whole earth
for getting help on an assignment.

However, the problem is interesting for other people: how to make a
double
linked list of tasks.

> We have to create a forward and backward linked list in Ada.
> 
> We have the following program (simplified here) :
> ---------------------------------------------------------------------------

-- added declarations
type CELLULE;
type CELLPOINTER is access CELLULE;

> 
> task type CELL is
     -- added entry
     entry GET_LINKS (MYSELF : in CELLPOINTER;
                      PREVIOUS : in CELLPOINTER);
>    entry X_IN (in_v : in INTEGER);
>    entry Y_OUT;
> end CELL;
> 
> type CELLULE is
> record
>   T : CELL;
> end record;
> 
-- remove the following declaration
> type CELLPOINTER is access CELLULE;
> 
> task body CELL is
-- add the following declaration
    currentLink : CELLPOINTER;
>   forwardLink : CELLPOINTER;
>   backwardLink : CELLPOINTER;
> begin
-- Add the following statements at the beginning
      accept GET_LINKS (MYSELF : in CELLPOINTER;
                        PREVIOUS : in CELLPOINTER) do
         currentLink := MYSELF;
         backwardLink := PREVIOUS;
      end;
> [...]
>         forwardLink := new CELLULE;
-- add the following statement
          forwardLink.T.GET_BACKWARD_LINK (MYSELF => ForwardLink,
                                           PREVIOUS => currentLink);
>           -- we should give the new cell a pointer to "this"
>         -- backwardLink := a pointer to the previous cell
> [...]
> end CELL;
> ---------------------------------------------------------------------------
> 
> We have no problem for the forward link, but for the backward link, we
> need to know the reference of the current
> task ("Current" in Eiffel, "this" in C++), to be able to pass it to the task
> that we create...
> 
> Does anyone know the solution ? HELP !!!
> 
>         Richard
> 
> PS: We don't want an object oriented solution.

The solution I just exposed is not OO at all!

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