skylighting

A Haskell syntax highlighting library with tokenizers derived from KDE XML syntax highlighting descriptions.

A command-line highlighter program, skylighting, is also provided.

This project is divided up into five packages:

• skylighting-core: this provides KDE XML parsing, data types, and a tokenizer. This includes the core functionality of the skylighting project licensed under the BSD3 license, along with the KDE XML files, some of which are licensed under the LGPL or GPL. This package does not provide any built-in parsers corresponding to the XML descriptions, however. For that, use skylighting.
• skylighting-format-ansi: this provides formatters for rendering skylighting tokens as colored ANSI text.
• skylighting-format-blaze-html: this provides formatters for rendering skylighting tokens as HTML, using the blaze-html library.
• skylighting-format-latex: this provides formatters for rendering skylighting tokens as LaTeX.
• skylighting: this exposes the skylighting-core API and ANSI, HTML, and LaTeX formatters, and also provides bundled Haskell parser modules derived from the XML descriptions in the core package. This package is entirely licensed under the GPL.

Motivation

This library is the successor to highlighting-kate, which had some problems that were difficult to resolve given its architecture.

In highlighting-kate, the XML syntax descriptions were converted into individual parsec parsers, which were then compiled. This made it difficult to handle IncludeRules properly without circular imports. There was also no way to load a syntax description dynamically.

Skylighting, by contrast, parses the XML syntax descriptions into Haskell data structures, which are then interpreted by a "tokenize" function. IncludeRules can now be handled properly, and users can add new syntax descriptions dynamically. It is also now possible to convert .theme files directly into styles.

Skylighting is also faster than highlighting-kate, by a factor of 3 in some cases.

Installing

To install the latest release from Hackage, do

stack install skylighting

or

cabal install skylighting

If you want the command-line tool, set the executable flag using --flag "skylighting:executable" in stack or -fexecutable in cabal.

The release tarball for the skylighting package includes generated files not present in this repository. Building from this repository is a two-step process. In the first step we build the skylighting-core package, which provides a program, skylighting-extract, which reads XML syntax highlighting definitions from the xml directory and writes Haskell source files. In the second we actually build the skylighting package.

Using cabal:

# First, build skylighting-extract
cabal build -fexecutable skylighting-core
# This will print the path of the built executable.
# Replace $EXE with this path in the following steps
# Now, generate the syntax files
cd ../skylighting
$EXE ../skylighting-core/xml
cabal install -fexecutable

Using stack:

stack build --flag skylighting-core:executable skylighting-core
cd skylighting
stack exec skylighting-extract -- ../skylighting-core/xml
cd ..
stack install --flag skylighting:executable

Command-line tool

A command-line executable, skylighting, is installed if the executable cabal flag is set in building.

For help, skylighting --help.

Adding new syntaxes

To compile with additional syntaxes, simply add the syntax definition (XML) file to the xml directory of the skylighting-core package and repeat the bootstrap build described above.

Note that both the library and the executable can dynamically load syntax definitions, so you may not need to compile them in. If you prefer this approach, you can use the skylighting-core package directly which provides the XML files without the generated code produced by the bootstrap process described above.

If the syntax definition you are adding is not already in the KDE repository, please submit it upstream so it can be included there. You can do that here, providing the file (or changes) and a test: https://invent.kde.org/frameworks/syntax-highlighting/-/merge_requests. Here is a sample merge request: https://invent.kde.org/frameworks/syntax-highlighting/-/merge_requests/20/diffs. If creating a proper merge request is too much work, at least submit an issue to https://invent.kde.org/frameworks/syntax-highlighting/-/issues alerting the KDE developers of the availability of a new or changed syntax definition; they can then decide whether to integrate it.

We normally pull changes in syntax definitions from upstream before each release.

License

The skylighting package is licensed under the GPL because some of the XML syntax descriptions from which its tokenizers are generated are GPL-licensed. However, the skylighting-core package, which provides the core types and functions of this project is licensed under the BSD3 license and bundles the GPL-licensed XML files separately.

The KDE project now recommends that new syntax highlighting files be MIT licensed.

References

Kate syntax highlighting documentation: https://docs.kde.org/stable5/en/kate/katepart/highlight.html

Kate highlighting definitions: KDE repository