Re: Programming for the World in Ada95

["Nick Roberts" <nickroberts@callnetuk.com>]

I was going to write an extensive reply to this one, but (I hear you sigh
with relief ;-)  I've cut it down to the following brief recommendations.

1. Introduce one package which declares an abstract root tagged type to
represent a piece of text, and a function to turn the object into actual
(Unicode) text. E.g.:

    package International.Text is

        type Root_Text_Piece is abstract tagged private;

        function Image (Piece: in Root_Text_Piece) return Wide_String is
abstract;

    end;

2. Derive types (in child or other packages, as appropriate) which
correspond to actual text messages. You must implement the 'Image' function
for each. Use an enumerated type as the basic message selector, and have a
derived type (its extension part) contain a component of this enumerated
type. The type can be further parametised in the same way, as necessary.

You can often avoid having to parameterise things too much by recasting your
output in a form which moves the parametised bits (e.g. numbers) out from
being embedded in the text. For example, instead of saying "there were 16
errors, of which 9 matter", you could say "Total number of errors:      16"
on one line, and "Number of critical errors:       9" on the next line,
perhaps. This style often tends to be neater, easier to read, easier to
program, easier to maintain and change, and generally avoids the necessity
for messing around with singular and plural forms.

3. Introduce a package (maybe generic) which implements message retrieval
from a configuration file or (much better) a database table. If your project
is divided into separate modules, being developed independently to some
extent (or simply if the program is very large), make sure you have
facilities for each module's person/team to add and delete messages to/from
the file/table independently of one another. Add a package that allows you
to list the enumeration literals that are message selectors against their
corresponding file/table messages (and keys). Maybe add 'fallback' code that
uses an internal message table in the event the configuration file/table
cannot be opened.

--
Nick Roberts
http://www.adapower.com/lab/adaos