Re: if statements

["Ken Garlington" <Ken.Garlington@computer.org>]

"Duncan Sands" <sands@topo.math.u-psud.fr> wrote in message
news:E13vbW9-0000DP-00@Baldrick...

: Here
: is a code snippet using the Beer oriented methodology (which naturally
: reflects the life style of many students) that swaps the values of two
: integers A and B if A is the greater value.  It uses an if statement.

Well, this doesn't seem right. In particular:

:       type Beer is new Integer;
-- this should be Natural; the -1 trick is no excuse (see below).

:       type Hand is (Left_Hand, Right_Hand);
-- this should be type What_I_Call_My_Hands
-- there should be a type Hand which is an access to Beer_Mug (see below)
-- there should be a type Hands which is an array (What_I_Call_My_Hands) of
Hand.

:       Mugs : array (Hand) of Beer_Mug;
-- this should be two separate mugs, since a particular mug is not
intrinsically tied to a particular Hand

:       type Table is record
:          Mug : Beer_Mug;
:       end record;
-- clearly, Table should be an array (or set) of Beer_Mugs, since a Table
could
-- hold more than one Beer_Mug.

:       procedure Move_Mug (From, To : Hand) is
:       begin
:          if From = To or Mugs (From).Refreshing_Fluid = -1 then
-- Ack! Arbitrary constants! Much better to allow a Hand to be set to null
-- explicitly when it isn't accessing anything.
-- Also, need to check that To is empty.

:             raise Tasking_Error;
-- should really declare a new Drunken_Fool exception rather than using
-- predefined exception