The main ideas around Isabelle/PIDE go back to summer 2008. This is an overview of what has been achieved in the past 9 years, with some prospects for the future. Where can we go from here as Isabelle community? (E.g. towards alternative front-ends like Visual Studio Code; remote prover sessions “in the cloud”; support for collaborative editing of large formal libraries.) Where can we go as greater ITP community (Lean, Coq, HOL family)?
Here are some notable VSCode projects that were briefly mentioned in the talk:
Here is an interesting (draft) paper about Social Network structures in the Isabelle and Coq community, based on the main mailing lists of the two systems:
J. Fleuriot, S. Obua, Ph. Scott: Social Network Processes in the Isabelle and Coq Theorem Proving Communities.arXiv:1609.07127, September 2016.
Just a few comments of mine:
The isabelle-users mailing list is still the main forum for Isabelle users, but Stackoverflow is gaining more and more importance. Note that I helped to bring it in form in Mar-2013 (earning a badge for 30 days of continuous activity :-), but I am rarely participating there now, because I am too busy with the classic mailing lists.
The seasonal peaks on isabelle-users in Fig. 1 are due to the release process, which happens approx. every 8-10 months. In 2012, I started to make discussion of release candidates fully public on isabelle-users; before it was confined to isabelle-dev, which is also open to everyone, but has fewer participants.
Page 12: “This seems to indicate that there is some clear separation of expertise when it comes to the tool.” This is correct and follows a general principle of Isabelle development: there are areas of undisputed “experts” for certain parts of the system. Thus there is a clear responsibility to make that thrive in the long term. Often this assignment is a consequence of starting that area in the first place, or investing significant work in upgrading it (e.g. by a designated PhD or research project). My recurring appearance on Sledgehammer threads is mainly technological: I am responsible for underlying infrastructure for parallel ML programming and the Prover IDE; it also overlaps with overall system integration and release management due to the add-on ATP and SMT systems.
In recent years, I have economized my appearance on isabelle-users as follows:
Incoming messages are marked as important, when the topic overlaps with my areas of expertise. I rarely answer on the spot.
After some days, weeks, or months, I revisit marked message and make sure that questions are actually answered, or add a few remarks to discussion threads.
During the release candidate phases, I revisit all marked messages back to the previous release (or even one before that), to make sure that old technical problems are solved or remain in a reasonably well-defined state.
This means the mailing list also serves as an “issue tracker”. I’ve made some experiments with an explicit tracker just for the release process, but there was very little participation. Trackers tend to become a long-term storage for well-known and unresolved problems.
Microsoft is more and more becoming an Open Source company, e.g. it has joined the Linux foundation as Platinum member in November 2016. A notable Open Source project by Microsoft is Visual Studio Code: under the slogans “Code editing. Redefined. Free. Open Source. Runs everywhere.” it provides a very interesting editor framework, as a desktop application based on Node.js and TypeScript.
Isabelle/VSCode is now following this trend: I have spent some weeks in December 2016 / January 2017 with VSCode, using a little bit of TypeScript and implementing the new Language Server Protocol in Isabelle/Scala. The subsequent screenshot shows formal annotations produced by Isabelle/PIDE in the usual manner, while the editor rendering is all done by VSCode. For more information, see the report Isabelle/VSCode in January 2017.
On 28-Oct-2016 the release candidate Isabelle2016-1-RC1 was published. Serious testing by users is now required, to expose remaining problems.
On 06-Nov-2016 the release candidate Isabelle2016-1-RC2 was published. Various details have been consolidated.
On 22-Nov-2016 the release candidate Isabelle2016-1-RC3 was published. More fine points have been consolidated. A component for the new experimental Nunchaku tool has been included.
On 27-Nov-2016 the release candidate Isabelle2016-1-RC4 was published. It introduces the following important last-minute changes:
Prover IDE: more aggressive flushing of machine-generated input
Sledgehammer: MaSh is faster and less likely to hang seemingly forever
fine-tuning of Isabelle/LaTeX typesetting
On 08-Dec-2016 the release candidate Isabelle2016-1-RC5 was published, presumably the last one. It introduces the following important last-minute changes:
more uniform automatic indentation (empty vs. non-empty lines)
fewer tracing/warning messages in some proof tools
The Isabelle release process is subject to the laws of causality: release candidates can be modified, but the final release remains final. Testing needs to happen in the weeks before the final release, not after it.
Isabelle is usually positioned as environment for interactive and automated theorem proving, but its Prover IDE (PIDE) may be used for regular program development as well. Standard ML is particularly important here, since it is the bootstrap language of Isabelle/ML (i.e. SML with many add-ons) and Isabelle/Pure (i.e. the logical framework).
The ML IDE functionality of Isabelle + Poly/ML is manifold:
Continuous feedback from static analysis and semantic evaluation is already available for years, e.g. Isabelle2014 (August 2014). It is a corollary of how PIDE interaction works, and of the integration of the Poly/ML compiler into that framework. Source files are statically checked and semantically evaluated while the user is editing. The annotated sources contain markup about inferred types, references to defining positions of items etc.
Source-level debugging within the IDE is new in Poly/ML 5.6, which is bundled with Isabelle2016 (February 2016). The Prover IDE provides the Debugger dockable to connect to running ML threads, inspect the stack frame with local ML bindings, and evaluate ML expressions in a particular run-time context. See also here.
IDE support for the Isabelle/Pure bootstrap process is new technology for the coming release of Isabelle2016-1 (December 2016). The ROOT.ML file acts like a quasi-theory in the context of theory ML_Bootstrap: this allows continuous checking of all loaded ML files. The theory file is presented with a modified header to import Pure from the running Isabelle instance.
It is also possible to modify standalone SML projects, to edit the sources freely in the ML IDE. For example, MetiTarski can participate after some trivial changes of its ROOT.ML file.
Overall, we move more and more to an integrated framework for development of formal-reasoning tools, but other applications are admissible as well.
The Slides are available, together with their sources (which are required for the live system demo).
Interactive theorem proving was historically tied to the read-eval-print loop, with sequential and synchronous evaluation of prover commands given on the command-line. This user-interface technology was adequate when Robin Milner introduced his LCF proof assistant in the 1970s, but today it severely restricts the potential of multicore hardware and advanced IDE front-ends.
The Isabelle Prover IDE breaks this loop and retrofits the read-eval-print phases into an asynchronous model of document-oriented proof processing. Instead of feeding a sequence of commands into the prover process, the primary interface works via edits over immutable document versions. Execution is implicit and managed by the prover in a timeless and stateless manner, making adequate use of parallel hardware.
PIDE document content consists of the theory sources (with dependencies via theory imports), and auxiliary source files of arbitrary user-defined format: this allows to integrate other languages than Isabelle/Isar into the IDE. A notable application is the Isabelle/ML IDE, which can be also applied to the system itself, to support interactive bootstrapping of the Isabelle/Pure implementation.
Further tool integration works via “asynchronous print functions” that operate on already checked theory sources. Thus long-running or potentially non-terminating processes may provide spontaneous feedback while the user is editing. Applications range from traditional proof state output (which often consumes substantial run-time) to automated provers and dis-provers that report on existing proof document content (e.g. Sledgehammer, Nitpick, Quickcheck in Isabelle/HOL). It is also possible to integrate “query operations” via additional GUI panels with separate input and output (e.g. for manual Sledgehammer invocation or find-theorems).
Thus the Prover IDE orchestrates a suite of tools that help the user to write proofs. In particular, the classic distinction of ATP and ITP is overcome in this emerging paradigm of Integrated Theorem Proving.