[m-dev.] for review: add mdb support for interactive queries

[Fergus Henderson]

On 11-Mar-1999, Peter Schachte <schachte at cs.mu.OZ.AU> wrote:
> 
> Hmmmmm.  What I proposed was basically the Quintus Prolog debugger
> model.  As I think about it, due to Mercury's overloading facilities
> another model seems better to me.  How about a model in which when
> you're debugging, it's as if you've implicitly imported every module in
> the application?  Whenever there's a conflict, you can explicitly
> module-qualify the goal.

That seems like a good UI to me.  And not to hard to implement.
The only difficulty as far as implementation goes is that you have
to read in a lot of interface files, so it might not be very efficient.

> When you're debugging a particular module, however, you are probably
> not interested in any modules other than the one you're debugging, the
> ones it imports, the ones they import, and so on. For such cases, it
> would be useful to focus on a particular module, and thereby limit
> visibility to modules recursively imported by the focus module.
> 
> How does that model sound?

Imports in Mercury are never transitive (well, modulo compiler bugs).
So I prefer to just include the directly-imported modules.
The user should be allowed to name additional modules to import
as well, though.

> So really all you have to do is add a debugger command to set the
> focus module, and always nest queries within that.  Maybe also a
> command to reset it to the default: the root module of the
> application.

Yep, sounds good.

So, I suggest the following commands at the `mdb>' prompt:

  mmc		<command name>
  mmc_options	<options list>

    These just let you override which version of mmc gets run and with which
    options.

  module	[<main-module> [<imported-modules list>]]
  import_module	<imported-modules list>
  use_module 	<used-modules list>

    The `module' command sets the focus module and resets the imported-modules
    list.  The `import_module' and `use_module' commands add modules to the
    lists of imported and used modules.

  query    	[<main-module> [<imported-modules list>]]
  cc_query 	[<main-module> [<imported-modules list>]]
  io_query 	[<main-module> [<imported-modules list>]]

    Alternatively, as an abbreviation, you can specify the focus module and
    imports as arguments to the `query', `cc_query' or `io_query' command. 
    (But you can't specify modules imported with `:- use_module' this way,
    you need to use the `use_module' command for that.)

    By default, there is no focus module, but all the modules in the
    application are imported.

In debug grade, there ought to be a default main/2 which just invokes
the debugger.  Then it would be nice to have

  load		<shared-lib>
  unload	<shared-lib>

    These would dynamically (re)load or unload a shared library.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3        |     -- the last words of T. S. Garp.