(See also general notes on proposals.)

Isabelle/Isar is ultimately about beatiful proof documents, not profane “proof scripts”. This explains why high-quality rendering of theory files in PDF-LaTeX has been part of the game from early on. In the past 15 years, the Isabelle document preparation system has been applied to produce numerous articles, books, theses etc. based on content that is formally checked in the logic (usually Isabelle/HOL). Here is an arbitrary example from AFP.
The Isabelle manuals are usually produced as Isabelle documents as well, e.g. see the sources in the directory src/Doc of the Isabelle distribution.

Traditional Isabelle document preparation is a side-effect of a session build process that is run in batch-mode; see also the Isabelle System manual, chapters 2 and 3. The main command-line tools for session management with document preparation are isabelle mkroot and isabelle build. This edit-typeset-preview cycle works, but feels a bit awkward today, where interactive theory and proof development with continuous checking in the Prover IDE (PIDE) is used routinely. So it his high time for various renovations and reforms of Isabelle document preparation as sketched below.

Immediate build process of documents within the Prover IDE.

There is no particular reason why LaTeX should be run via batch-mode tools on the command-line. The Prover IDE could take care of that interactively, with much shorter turnaround cycles of the edit-typeset-preview cycle. To achieve that, parts of the document preparation in Isabelle/ML need to be moved to Isabelle/Scala, and slightly generalized to become stateless and applicable to partial/unfinished document sources.

GUI panel for document preparation in Isabelle/jEdit.

This should allow to control document preparation in the IDE, e.g. to specify which parts of the document are presently interesting, or to change options for LaTeX and add-on tools.

Improved error reporting from LaTeX

LaTeX error output should be parsed and presented within the Prover IDE adequately, with proper error positions over the original source text. The notoriously obscure LaTeX log files need to be overcome.

Light-weight document markup as in Markdown / Commonmark with approximative preview in the source.

Instead of old-fashioned LaTeX markup like \begin{itemize} \item ... \end{itemize} there could be more direct indication of itemization in the source (with actual bullets from the Isabelle symbol repertoire). Using conventions from Markdown, it would approximate a preview of the final typesetting already in the source text. Enumerations and description lists could be done similarly. Note that there is no need for sections (which are already supported via explicit Isar commands), nor for hyperlinks and other formal inserts (which are already supported via document antiquotations).

Improved HTML output

A subset of document markup that fits into the limited Markdown / Commonmark format sketched above could be taken as starting point for better HTML presentation, with relatively modest ambitions and technical requirements. It is important to recall that “HTML” as such is a huge and vaguely defined collection of standards: producing portable output that looks nice on most browsers requires significant expertise or special tools, or both.

A few improvements have already made it into the repository after Isabelle2014. For example, the repository version Isabelle/872f330a0f8a provides support for BibTeX files in Isabelle/jEdit. In Isabelle/9986fb541c87 there is also support for @{cite} antiquotations, with formal links etc.

(See also general notes on proposals.)

“Cloud computing” is one of these buzzwords without any particular meaning, but the idea to run heavy-duty computations remotely is rather old: some “big-iron” in the background provides the CPU and memory resources for substantial applications, while the user interacts with the system via some small local terminal. Already in the classic days of Proof General (around 1999) it was common-place to run Emacs locally on a workstation and the prover process remotely on a server (via rsh). Alternatively it was possible to run both the editor and the prover remotely and use X11 as display protocol, which was especially important for the rather heavy XEmacs of that time.

This normal mode of distributed computing was almost forgotten, when the performance of local laptops and remote servers were approaching the same order of magnitude (due to the demands of the gaming industry). This was only an episode over a single decade, though, and we are already back to the traditional situation where local and remote machines can differ significantly. In 2014, typical mobile devices were limited to 2–8 CPU cores and 2–8 GB RAM. This is very little compared to low-end workstations or high-end servers, with something like 8–36 CPU cores and 32–512 GB RAM, or more.

Note that some big Isabelle applications already go beyond the possibilities of small machines with only 4–8 GB RAM, but for more memory Poly/ML process needs to be switched from 32-bit to 64-bit mode, which also doubles the memory demands. Thus there is a discontinuity here: stepping out of the “small device” category means to go for 16–32 GB RAM minimum.

This motivates the demand for remote prover connectivity for Isabelle and its Prover IDE (PIDE). The most basic approach is to run the internal socket connection for the PIDE protocol between ML and Scala over ssh. This should be sufficient for fast and reliable local networks. For non-local networks, there are the usual questions about bandwidth, latency, and reliability of the connection. The PIDE protocol requires relatively high bandwidth (which is easily provided by common DSL connections), but can afford high latency due to its asynchronous nature. Lack of reliability might turn out a real problem, though: resetting a lost TCP/IP connection naively means to restart the prover process and recheck the whole session from start, which could take minutes or hours.

Thus a more advanced approach would keep both the ML and Scala side of PIDE together on the server. Remote access then works via a separate PIDE display protocol, which is postulated here and still needs to be defined and implemented. Depending on active buffers and open text areas in the editor, the remote side would provide continuous access to incoming PIDE document markup, without demanding persistent management of the whole PIDE state locally. Loosing the connection would merely mean to reconnect the IDE to the remote Isabelle/Scala/ML component, which keeps running indefinitely.

Thus the mode of operation becomes more like the re-connection facility of VNC or RDP (but not X11). Of course it is already possible today with Isabelle2014 to use VNC or RDP for a completely remote ML/Scala/IDE process, but remote ML/Scala and local IDE would make this more comfortable for the user, with better graphics performance and reactivity.

Taking this perspective of remote PIDE sessions one step further could mean to support low-bandwidth, high-latency, unreliable connections of mobile networks: sitting on a train with a laptop and local IDE, while re-connecting to a remote PIDE session on a big server, would really count as cloud computing. We should think here of editing whole libraries like AFP on the spot, with immediate feedback. A bit more efforts will be required to get there, though.

In summary, the following stages are possible, depending on the amount of resources spent on this subject:

1. Simple remote PIDE socket connection via ssh, usable for fast and reliable local networks. (The jEdit text editor already provides some means to manage ssh, so this merely requires the usual study of sources with subsequent tinkering and polishing to make it work smoothly.)
2. Separate PIDE display protocol where the editor is local and the Isabelle/Scala/ML session is remote. This should be usable for fast DSL network connections.
3. Support for smooth disconnection and re-connection for mobile networks.
4. Development of a completely different PIDE front-end that works on tablets or smart-phones (Android or iOS).

The last point is speculative: it merely sketches to horizon of what could eventually be targeted, if there were lots of resources and several enthusiastic people working on it.