[mercury-users] Mercury in academic teaching?

[Jonathan Morgan]

On 07/10/06, Kathryn Francis <francis at students.csse.unimelb.edu.au> wrote:
>
>
> On Sat, 7 Oct 2006, Jonathan Morgan wrote:
>
> > On 06/10/06, Jörg Roman Rudnick <joerg.rudnick at t-online.de> wrote:
> > > Is Mercury an option as introduction to logic programming?
> > >
> > > Personally very convinced, I am unsure about possible problems in
> > > teaching it as second (or third) language besides Java (and C#) to
> > > students of AI (at a course of study like 'master of business computing').
> > >
> >
> > As a student who is just studying Prolog, I do not believe that
> > Mercury is likely to be a good introductory logic programming language
> > for several reasons.  The main one is very simple - Mercury was not
> > designed for simplicity, but rather for performance and large-scale
> > Software Engineering.  In my opinion, this makes it a great language
> > for using to write real programs, but not for education, as even small
> > programs require understanding of Mercury's module system, type and
> > mode system (unless you use inference), and the I/O state.  On the
> > contrary, most Prologs do not require types, and have interpreters,
> > allowing them to be used in an exploratory manner quickly and easily -
> > which I feel is much better for education as an introduction to logic
> > programming.
>
> I'm a lab demonstrator for the subject 'Logic and Computation', which is
> the subject that teaches Prolog in our department, and I find that one of
> the main things that confuses people learning Prolog is the absence of
> types. I get questions like "How does Prolog know that this is supposed to
> be a tree?" all the time.

I have never felt like that - but I always wanted the types in to
start with, and I suppose I did have experience of Mercury before
using Prolog.

> It seems to me that you need to think about types and modes to write
> correct programs in prolog, and it's actually helpful for a novice to
> write them down explicitly, which is what Mercury forces you to do. Also
> having more static checking can be useful for novices because you get
> handy hints from the compiler in cases where the corresponding Prolog
> program would just fail or give a runtime error.

Some of the hints I have got from the compiler (with both Haskell and
Mercury) have been anything but handy.  However, I agree that you need
to think about the types to some extent - but do you really need to
know about `di` and `uo` modes? (`in` and `out` make fairly good
sense).  I would certainly prefer the compiler to prove my program is
deterministic, rather than having the predicate just fail because my
types were slightly wrong, or produce multiple solutions in wierd
contexts.

> That said, I think the decision to teach Mercury or Prolog really depends
> on exactly what you're wanting to get across. If you just want to teach
> logic programming concepts, then maybe Mercury is the way to go, but if
> you want to also introduce students to an interpreted style language
> geared towards fast development, or you want to introduce a weakly typed
> language to contrast with Java, then clearly Prolog is better.

Make that 'exploratory development' - my guess is that you can
probably develop a large software system much faster in Mercury than
in Prolog, because the language features fairly quickly start becoming
an aid, whereas in Prolog it is the other way around.

I am unaware of any courses teaching Mercury as an introduction to
logic programming, so I would be interested in seeing how it worked.
My feeling is that it would work a lot better with students who have
already studied a strongly typed functional language, as far less time
would have to be spent explaining the type system.  Mercury would also
have the strong advantage that the lecturer wouldn't have to point out
all the problems with the non-logical features of Prolog, as seems to
happen frequently in our lectures.

Jon

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