Multidimensional array vs. array of array

[lutz@iks-jena.de (Lutz Donnerhacke)]

How does a skilled Ada programmer define a return type containing a
multidimensional array? Of course, the simple solution works:

  type Equations is array (Rows range <>, Columns range <>) of Number;
  type Workspace (row : Rows; col : Columns) is record
    eqs : Equations (Rows'First .. row, Columns'First .. col);
    ... some more stuff ...
  end record;
  function Init_Workspace return Workspace;

But this approach fails miserably on extracting a single row from the result
as well as on construction the result in a recursive function.

I do not found a way to define this type as an array of arrays despite
writing a generic package over the maximum values:
  generic
     type Columns is range <>;
  package
     type Equation  is arry (Columns) of Number;
     type Equations is array (Rows range <>) of Equation;
     type Workspace (row : Rows) is record
        eqs : Equations (Rows'First .. row);
        ... some more stuff ...
     end record;
     function Init_Workspace return Workspace;
  end package;

But this approach does not work for a situation where determining the
resulting constraints is equivalent to simulating the Init_Workspace
recursion. This should be avoided: Error-prone, duplicated and slightly
modified code.

Any idea?