Hi Nick
nick thomas wrote:
Well, that brings me to my next question. I'd like to start writing an
editor, as I said I would. Will Epigram2's editor/elaborator interface
be completely different from Epigram1's?
Yes. For a start, there'll be one! In Epigram 1, the editor just
provides a rendering of the elaborator state. The elaborator is
responsible for knowing where your cursor sits in a shed and other such
details, a world away from typechecking: it was very cheap and it
sort-of works, but it's very hard to build on. In fact, that's a fairly
reasonable summary of the state of Epigram 1, more generally.
More to the point, would it be wasted effort to start hacking on Epigram1?
For all but the very cheapest experiments or tweaks, yes. Epigram 1 is
inching towards the scrap heap.
If so, is the editor/elaborator interface for Epigram2 relatively
fleshed out by now? Or, more to the point, would it be wasted effort
to start hacking on Epigram2?
The basic shape is there, but it isn't very documented. Here's where to
start looking:
http://sneezy.cs.nott.ac.uk/epigram/current/doc/index.html
The basic picture is that Editor and Elaborator live in different
threads and have a communication format based on the concrete syntax.
The shared state is a big lump of concrete syntax with uniquely labelled
nodes. The basic Editor-Elaborator message is 'replace node x with this
piece of concrete syntax'. The basic Elaborator-Editor message is 'node
x has been replaced by this piece of node-labelled concrete syntax'. The
process kicks off with the Elaborator issuing the Editor with its root
node. We don't fix any style of interaction: it could be batch-mode
(replace root with whole program) or some fab asynchronous thing.
That said, the concrete syntax is already quite an evolved
representation in the life of a program, so lots of 'front end' stuff
has to happen in the Editor. However, we have a hierarchy of tools which
refine input all the way from strings to tokens to 2D documents to
syntax to syntax-with-resolved-scope (the Elaborator is never told the
user's name choices!), which leaves it up to the Editor-author to choose
what to trade in. An editor written in something other than Haskell
would require a suitable Haskell stub.
Now, we're currently refactoring the guts of Epigram 2 as we shift over
from cvs to darcs. House style is now to write lhs2TeX source, which
should at least encourage better documentation. This effort should
deliver a dummy elaborator fairly soon---one which communicates sensibly
with an editor but doesn't actually typecheck anything. The real thing
will take a bit longer. I wish I knew how long, but it's very hard to
predict how much hacking we'll manage to fit in around everything else
that's going on.
So, Epigram 2 would be the target to go for; the general set-up is
already sketched out, so you could at least start planning; once the
current move to is complete, we'll have better documentation; shortly
after that, we'll have a thing (albeit a dummy) you can actually link to.
Thank you for your enthusiasm!
All the best
Conor
