[GUI] Proposal Proposal: haskell-gui addendum to haskell

[Simon Peyton-Jones]

| Perhaps the best would be to use an Object-IO like interface
| with mvars as proposed by Simon Peyton-Jones, simply because it's
| higher level than raw gui-calls and the Clean folks have used
| it cross-platform in a few real apps.

Indeed. My impression is that we won't get far trying to design a truly
high-level declarative GUI toolkit, because there just isn't enough
consensus on what it should look like. There have been a number of very
interesting experiments, but none has captured everyone's attention.  I
just don't think we yet know the answer here, though I am hopeful that
further exploration will eventually uncover it (or them).

Meanwhile, lacking the Final Answer, we need a practical solution.  One
possibility would be to adopt some multi-platform toolkit like Gtk, and
provide a Haskell wrapper for each function.  Several such bindings
exist.  But that is (a) terribly low level, (b) very toolkit-specific.
I think we can do a bit better.

My personal favourite is the Clean Object-IO story: it's higher level
and more abstract than just a simple imperative veneer over (eg) Gtk,
but it's still low level enough that its not hard to implement.
Furthermore, the Clean folk have a developed over a decade, so they have
*lots* of experience of using it in real applications.  Let's take
advantage of their wisdom; I would be surprised if we could do better if
we started from a blank sheet of paper.

So I propose the Clean Object-IO approach as a reasonable compromise
starting point for the programming interface.  (I'm entirely agnostic
about what is the most suitable underlying C library to use; indeed, the
choice of that library should ideally be un-discoverable to the
programmer.)  I say "starting point" because there are still plenty of
design choices to be made.  For example, to use the Clean "local state"
idea or use MVars?  This choice is discussed in the paper that Peter
Aachten and I wrote:
=09
http://research.microsoft.com/~simonpj/Papers/haskellobjectio.htm
I'm sure there are many other choices.

This suggestion is not based on deep study.  Maybe others have better
ideas.  But I counsel against trying to find a truly high-level design.
Worse is better.

Simon