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A collection of tools for writing technical documents that mix Coq code and prose.

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Alectryon

A library to process Coq snippets embedded in documents, showing goals and messages for each Coq sentence. Also a literate programming toolkit for Coq. The goal of Alectryon is to make it easy to write textbooks, blog posts, and other documents that mix Coq code and prose.

Alectryon is typically used in one of three ways:

  • As a library, through its Python API
  • As a reStructuredText extension, allowing you to include annotated snippets into your reStructuredText documents. During compilation, Alectryon collects all .. coq:: blocks, feeds their contents to Coq, and incorporates the resulting goals and responses into the final document.
  • As a standalone compiler, allowing you to include prose delimited by special (*| … |*) comments directly into your Coq source files (in the style of coqdoc). When invoked, Alectryon translates your Coq file into a reStructuredText document and compiles it using the standard reStructuredText toolchain.

For background information, check out the quickstart guide on the MIT PLV blog, the SLE2020 paper (open access) and its live examples, or the conference talk.

Alectryon is free software under a very permissive license. If you use it, please remember to cite it, and please let me know!

Some examples of use in the wild are linked at the bottom of this page. Please add your own work by submitting a PR!

Setup

Dependencies (OCaml, Python 3):
opam install "coq-serapi>=8.10.0+0.7.0"
python3 -m pip install --user --upgrade pygments dominate beautifulsoup4 docutils

The core library only depends on coq-serapi. dominate is used in alectryon.html to generate HTML output, and pygments is used by the command-line application for syntax highlighting. reStructuredText support requires docutils; Coqdoc support requires beautifulsoup4. Support for Coq versions follows SerAPI; Coq ≥ 8.10 works well and ≥ 8.12 works best.

Usage

As a standalone program

Recipes

Try these recipes in the recipes directory of this repository (for each task I listed two commands: a short one and a longer one making everything explicit):

Generate an interactive webpage from a literate Coq file with reST comments (Coqdoc style):
../alectryon.py literate.v
../alectryon.py --frontend coq+rst --backend webpage literate.v -o literate.html
Generate an interactive webpage from a plain Coq file (Proof General style):
../alectryon.py --frontend coq plain.v
../alectryon.py --frontend coq --backend webpage plain.v -o plain.v.html
Generate an interactive webpage from a Coqdoc file (compatibility mode):
../alectryon.py --frontend coqdoc literate.v
../alectryon.py --frontend coqdoc --backend webpage literate.v -o literate.html
Compile a reStructuredText document containing .. coq:: blocks (coqrst style):
../alectryon.py literate.v.rst
../alectryon.py --frontend rst --backend webpage literate.v.rst -o literate.html
Translate a reStructuredText document into a literate Coq file:
../alectryon.py literate.v.rst -o literate.v
../alectryon.py --frontend rst --backend coq+rst literate.v.rst -o literate.v
Translate a literate Coq file into a reStructuredText document:
../alectryon.py literate.v -o literate.v.rst
../alectryon.py --frontend coq+rst --backend rst literate.v -o literate.v.rst
Record goals and responses for fragments contained in a JSON source file:
../alectryon.py fragments.json
../alectryon.py --frontend json --backend json fragments.json -o fragments.io.json
Record goals and responses and format them as HTML for fragments contained in a JSON source file:
../alectryon.py fragments.json -o fragments.snippets.html
../alectryon.py --frontend json --backend snippets-html fragments.json -o fragments.snippets.html

Command-line interface

python3 alectryon.py [-h] […]
           [--frontend {coq,coq+rst,json,rst}]
           [--backend {coq,coq+rst,json,snippets-html,webpage}]
           input [input ...]

  • Each input file can be .v (a Coq source file, optionally including reStructuredText in comments delimited by (*| … |*)), .json (a list of Coq fragments), or .rst (a reStructuredText document including .. coq:: blocks). Each input fragment is split into individual sentences, which are executed one by one (all code is run in a single Coq session).

  • One output file is written per input file. Each frontend supports a subset of all backends.

    • With --backend webpage, output is written as a standalone webpage named <input>.html (for coq+rst inputs) or <input>.v.html (for plain coq inputs). This is useful for debugging and to get a quick sense of how Alectryon works.

    • With --backend snippets-html, output is written to <input>.snippets.html as a sequence of <pre class="alectryon-io"> blocks, separated by <!-- alectryon-block-end --> markers (there will be as many blocks as entries in the input list if input is a .json file).

    • With --writer json, output is written to <input>.io.json as a JSON-encoded list of Coq fragments (as many as in input if input is a .json file). Each fragment is a list of records, each with a _type and some type-specific fields. Here is an example:

      Input (minimal.json):
      ["Example xyz (H: False): True. (* ... *) exact I. Qed.",
 "Print xyz."]
      Output (minimal.json.io.json) after running ./alectryon.py --writer json minimal.json:
      [ // A list of fragments
  [ // Each fragment is a list of records
    { // Each record has a type, and type-specific fields
      "_type": "sentence",
      "sentence": "Example xyz (H: False): True.",
      "responses": [],
      "goals": [
        {
          "_type": "goal",
          "name": "2",
          "conclusion": "True",
          "hypotheses": [
            {
              "_type": "hypothesis",
              "name": "H",
              "body": null,
              "type": "False"
            }
          ]
        }
      ]
    },
    {"_type": "text", "string": " (* ... *) "},
    {"_type": "sentence", "sentence": "exact I.", "responses": [], "goals": []},
    {"_type": "text", "string": " "},
    {"_type": "sentence", "sentence": "Qed.", "responses": [], "goals": []}
  ],
  [
    {
      "_type": "sentence",
      "sentence": "Print xyz.",
      "responses": ["xyz = fun _ : False => I\n     : False -> True"],
      "goals": []
    }
  ]
]

Use ./alectryon.py --help for full command line details.

As a library

Use alectryon.core.annotate(chunks: List[str]), which returns an object with the same structure as the JSON above, but using objects instead of records with a _type field:

>>> from alectryon.core import annotate
>>> annotate(["Example xyz (H: False): True. (* ... *) exact I. Qed.", "Print xyz."])
[
    [CoqSentence(sentence='Example xyz (H: False): True.',
                 responses=[],
                 goals=[
                     CoqGoal(
                         name='2',
                         conclusion='True',
                         hypotheses=[
                             CoqHypothesis(name='H',
                                           body=None,
                                           type='False')
                         ])
                 ]),
     CoqText(string=' (* ... *) '),
     CoqSentence(sentence='exact I.', responses=[], goals=[]),
     CoqText(string=' '),
     CoqSentence(sentence='Qed.', responses=[], goals=[])],

    [CoqSentence(sentence='Print xyz.',
                 responses=['xyz = fun _ : False => I\n     : False -> True'],
             goals=[])]
]

The results of annotate can be fed to alectryon.html.HtmlGenerator(highlighter).gen() to generate HTML (with CSS classes defined in alectryon.css). Pass highlighter=alectryon.pygments.highlight_html to use Pygments, or any other function from strings to dominate tags to use a custom syntax highlighter.

As a docutils or Sphinx module

With blogs (Pelican, Nikola, Hugo, etc.)

Include the following code in your configuration file to setup Alectryon's docutils extensions:

import alectryon.docutils
alectryon.docutils.setup()

This snippet registers a .. coq:: directive, which feeds its contents to Alectryon and displays the resulting responses and goals interleaved with the input and a :coq: role for highlighting inline Coq code. It also replaces the default Pygments highlighter for Coq with Alectryon's improved one, and sets :coq: as the default role. See help(alectryon.docutils) for more information.

To ensure that Coq blocks render properly, you'll need to tell your blogging platform to include alectryon.css. Using a git submodule or vendoring a copy of Alectryon is an easy way to ensure that this stylesheet is accessible to your blogging software. Alternatively, you can use alectryon.html.copy_assets. Assets are stored in alectryon.html.ASSETS.PATH; their names are in alectryon.html.ASSETS.CSS and alectryon.html.ASSETS.JS.

By default, Alectryon's docutils module will raise warnings for lines over 72 characters. You can change the threshold or silence the warnings by adjusting alectryon.docutils.LONG_LINE_THRESHOLD. With Pelican, use the following snippet to make warnings non-fatal:

DOCUTILS_SETTINGS = {
    'halt_level': 3, # Error
    'warning_stream': None # stderr
}

I test regularly with Pelican; other systems will likely need minimal adjustments.

With Sphinx

For Sphinx, add the following to your conf.py file:

import os
import sys
sys.path.insert(0, os.path.abspath('../path/to/alectryon/repo/'))

extensions = ["alectryon.sphinx"]

If left unset in your config file, the default role (the one you get with single backticks) will be set to :coq:. To get syntax highlighting for inline snippets, create a docutils.conf file with the following contents along your conf.py file:

[restructuredtext parser]
syntax_highlight = short

Controlling output

The .. coq:: directive takes a list of space-separated flags to control the way its contents are displayed:

  • One option controls whether output is folded (fold) or unfolded (unfold). When output is folded, users can reveal the output corresponding to each input line selectively.
  • Multiple options control what is included in the output. - in: Include input sentences (no-in: hide them) - goals: Include goals (no-goals: hide them) - messages: Include messages (no-messages: hide them) - out: Include goals and messages (no-out: hide them) - all: Include input, goals, and messages (none: hide them)

The default is all fold, meaning that all output is available, and starts folded. The exact semantics depend on the polarity of the first inclusion option encountered: x y z means the same as none x y z, i.e. include x, y, z, and nothing else; no-x no-y means all no-x no-y, i.e. include everything except x and y.

These annotations can also be added to individual Coq sentences (⚠ sentences, not lines), using special comments of the form (* .flag₁ … .flagₙ *) (a list of flags each prefixed with a .):

.. coq::

   Require Coq.Arith. (* .none *)      ← Executed but hidden
   Goal True. (* .unfold *)            ← Goal unfolded
     Fail exact 1. (* .in .messages *) ← Goal omitted
     Fail fail. (* .messages *)        ← Error message shown, input hidden

Extra roles and directives

For convenience, alectryon includes a few extra roles and directives:

  • :coqid: can be used to link to the documentation or definition of a Coq identifier in an external file. Some examples:

    By default, :coqid: only knows how to handle names from Coq's standard library (that is, names starting with Coq., which get translated to links pointing to https://coq.inria.fr/library/). To link to other libraries, you can add entries to alectryon.docutils.COQ_IDENT_DB_URLS, a list of tuples containing a prefix and a templated URL. The URL can refer to $modpath, the part before the last # or . in the fully qualified name, and $ident, the part after the last # or .. Here is an example:

    ("My.Lib", "https://your-url.com/$modpath.html#$ident")

    Alternatively, you can inherit from :coqid: to define new roles. The following defines a new :mylib: role, which assumes that its target is part of My.Lib:

    .. role:: mylib(coqid)
   :url: https://your-url.com/My.Lib.$modpath.html#$ident

Caching

The alectryon.json module has facilities to cache annotations. Caching has multiple benefits:

  1. Recompiling documents with unchanged code is much faster, since Coq snippets do not have to be re-evaluated.
  2. Deploying a website or recompiling a book does not require setting up a complete Coq development environment.
  3. Changes in output can be inspected by comparing cache files. Caches contain just as much information as needed to recreate input/output listings, so they can be checked-in into source control, making it easy to assess whether a Coq update meaningfully affects a document (it's easy to miss breakage or subtle changes in output otherwise, as when using the copy-paste approach or even Alectryon without caching).

To enable caching, chose a directory to hold cache files and assign its path to alectryon.docutils.CACHE_DIRECTORY (it can be the same directory as the one containing your source files, if you'd like to store caches alongside inputs). Alectryon will record inputs and outputs in individual JSON files (one .cache file per source file) in subdirectories of the CACHE_DIRECTORY folder.

Tips

Prettification

Programming fonts with ligatures are a good way to display prettified symbols without resorting to complex hacks. Good candidates include Fira Code and Iosevka (with the latter, add .alectryon-io { font-feature-settings: 'XV00' 1; } to your CSS to pick Coq-specific ligatures).

Passing arguments to SerAPI

When using the command line interface, you can use the -I, -Q, -R and --sertop-arg flags to specify custom SerAPI arguments, like this:

./alectryon.py -R . Lib --sertop-arg=--async-workers=4

When compiling reStructuredText documents, you can add custom SerAPI arguments in a docinfo section at the beginning of your document, like this:

:alectryon/serapi/args: -R . Lib -I mldir

To set SerAPI's arguments for all input files, modify AlectryonTransform.SERTOP_ARGS in alectryon.docutils. Here's an example that you could use in a Sphinx config file:

from alectryon.docutils import AlectryonTransform
AlectryonTransform.SERTOP_ARGS = ["-Q", "/coq/source/path/,LibraryName"]

Note that the syntax of SERTOP_ARGS is the one of sertop, not the one of coqc (ejgallego/coq-serapi#215).

Adding custom keywords

You can use alectryon.pygments.add_tokens to specify additional highlighting rules, such as custom tactic names. See help(alectryon.pygments.add_tokens) for more details.

When compiling reStructuredText documents, you can add per-document highlighting rules to the docinfo section at the beginning of your document, like this:

:alectryon/pygments/tacn: intuition_eauto simplify invert
:alectryon/pygments/tacn-solve: map_tauto solve_eq

Interactivity

Alectryon's HTML output doesn't require JavaScript for basic interactivity, but assets/alectryon.js implements keyboard navigation.

Authoring support

The etc/elisp folder of this directory includes an Emacs mode, alectryon.el, which makes it easy to switch between the Coq and reStructuredText views of a document.

Caching

To use Alectryon's caching facilities independently of its docutils module, instantiate the FileCache class of alectryon.json.

Building without Alectryon

The alectryon.minimal Python module provides trivial shims for Alectryon's roles and directives, allowing you continue compiling your documents even if support for Alectryon stops in the future.

Including custom JS or CSS in Alectryon's output

For single-page documents, you can use a .. raw:: directive:

.. raw:: html

   <script src="https://d3js.org/d3.v5.min.js" charset="utf-8"></script>
   <script src="https://dagrejs.github.io/project/dagre-d3/latest/dagre-d3.js"></script>

   <link rel="stylesheet" href="rbt.css">
   <script type="text/javascript" src="rbt.js"></script>

For documents with more pages, you can either move the .. raw part to a separate file and .. include it, or you can use a custom driver: create a new file driver.py and use the following:

import alectryon.html
import alectryon.cli

alectryon.html.ADDITIONAL_HEADS.append('<link rel="stylesheet" href="…" />')
alectryon.cli.main()

But for large collections of related documents, it's likely better to use Sphinx (or some other similar engine). In that case, you can use Sphinx' built-in support for additional JS and CSS: app.add_js_file(js) and app.add_css_file(css).

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A collection of tools for writing technical documents that mix Coq code and prose.

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