Path: utzoo!attcan!uunet!cs.utexas.edu!tut.cis.ohio-state.edu!mailrus!cornell!rochester!udel!mmdf
From: thywiss@csvax.cs.ukans.edu (John A. Thywissen)
Newsgroups: comp.sys.amiga
Subject: Callable Application Interfaces
Message-ID: <15323@louie.udel.EDU>
Date: 12 May 89 18:05:50 GMT
Sender: mmdf@udel.EDU
Lines: 56

#define PHILOSOPICAL_MODE 1

The discussion of file requester libraries, has brought up the notion of
modular functionality of a system.  This is a problem that can be
generalized beyond simply file requesters and the like.  Computer
scientists have been "chewing" on this type of problem for years.  One
solution, already mentioned on the net is the concept used in
Smalltalk--Abstract Data Types.

An abstract data type is a module defined in terms of an object, i.e. a
file requester, with operations on it, such as create a new requester,
display it, etc.  User programs of the object are NOT allowed to operate
on the object directly, only to ask the Abstract Data Type (ADT) to
perform operations in the user's behalf.  Amiga libraries are an
implementation of ADTs.

Now, not only can ADTs be useful for items such as scroll arrows, file
requesters, and the like, but also for larger objects like "a formatted
text file" (as produced by a word proccessor), a IFF ILBM picture (as
produced by your favorite paint program).  In the course of some
applications, such as a mail system, there may be call for an object
produced by another system.  So, your mail system should be able to say,
in a standard way, "Edit this text file and put the results here", just
as Rob Peck proposed a way for an application to say "Ask the user to
pick file and tell me what it is".

If there would be some standardized way to call these other modules then
there would no longer be dilemmas such as which text editor for messages
to stick in that wonderful mail system you are devloping.  (I like
MEmacs, but Joe (not his real name :-) ) would sooner be boiled in oil
then use any Emacs derivative.)  The application would just

  EdBase = OpenLibrary("STD_EDITOR:editor.library",0);
                                    /* Path & name stuff needs
                                       standardization, too */
  stdReturnCode = EditFile("T:draft_message");
  CloseLibrary(EdBase);

I propose the somehow, there should be a standardization effort for
callable interfaces to applications and that a registry, similar to
CATS's IFF registry, be set up.  Essentially, the interface
specification would amount to a ".fd" file and a corresponding AutoDoc.

Users then could just "drop in" whichever application/module they like
and run.

Another proposal (wow, two for the price of one!):  Perhaps even the
application could ask for "give me an IFF ANBM form", and the 'system'
could look up which programs were capable of producing that type of
object, and then ask the user which one to use.  (Another file
requester!!)
-------
John A. Thywissen                 <thywiss@csvax.cs.ukans.edu>
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