Re: disjoint ranges ?

[wayne lydecker <wlydeckr@pacbell.net>]

> wayne lydecker wrote:
> 
> >How about using a boolean array:
> >
> > with Text_IO;
> > procedure lunch is
> >   type Hours is new Integer range 0 .. 23 ;
> >   Lunch_Hours : array (Hours) of Boolean :=
> >     (7..9 => True, 12..14 => True, 19..21 => True, others => False);
> > begin
> >   if Lunch_Hours(7) then
> >     text_io.put_line("Lunch time");
> >   else
> >     text_io.put_Line("Get back to work");
> >   end if;
> > end;
> 
> This is one of those, "I can find a way to do it in my language," examples.
> We can ultimately solve any programming problem in any programming
> language (Yes, I exaggerate slightly), but this returns us to the issue of
> expressiveness versus expressibility.   Certain languages are more expressive
> of certain problems.   They directly map the solution space to the problem
> space.
> 
> The original post, if I read it correctly, was not concerned with the question,
> "Can such and such be accomplished," but rather, "Is there a syntax to
> directly express the solution to the given problem?"   Pat Rogers candidly
> and succinctly answered, "No."  That was a correct answer.
> 
> Richard Riehle

I see your point.  Mine was a simple solution but did not employ
sets.  To mimic the union of homogenous sets is relatively simple,
here is how I did it.  There are many more operators other than
"in" that could also be coded, but I suspect that that is the
reason it's not part of the language.

-- Wayne.

package Sets is
  type Set_Type is array (1..2) of Integer;
  type Set_Array_Type is array (Positive range <>) of Set_Type;

  function Is_In (Value     : Integer;
                  Set_Array : Set_Array_Type)
                  return Boolean;
end;
----------
package body Sets is
  function Is_In (Value     : Integer;
                  Set_Array : Set_Array_Type)
                  return Boolean is
  begin
    for SA in Set_Array'range loop
      if Value >= Set_Array(SA)(1) and
         Value <= Set_Array(SA)(2) then
        Return True;
      end if;
    end loop;
    Return False;
  end;
end;
------------
with Sets;
with Text_IO;
procedure Lunch is
  Lunch_Hours : constant Sets.Set_Array_Type := ((7,9), (12,14), (19,21));
begin
  if Sets.Is_In (7, Lunch_Hours) then
    text_io.put_line("Lunch time");
  else
    text_io.put_Line("Get back to work");
  end if;
end;