syntax highlighting library

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LTS Haskell 8.6:
Stackage Nightly 2017-03-29:
Latest on Hackage:0.3.1


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

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


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.


To install the latest release from Hackage, do

stack install skylighting


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 tarballs include generated files not present in this repository. Building from this repository is a two-step process. In the first step we build 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 library.

Using stack:

make bootstrap

Using cabal:

cabal install -fbootstrap --disable-optimizations
cabal run skylighting-extract -- xml/*.xml
cabal install -f-bootstrap --disable-optimizations

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 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.


Skylighting is licensed under the GPL, because some of the xml syntax descriptions from which its tokenizers are generated are GPL-licensed.


Kate syntax highlighting documentation:

Kate highlighting definitions:


Revision history for skylighting

0.3.1 -- 2017-02-28

  • Use handwritten parser for Float instead of regex. Fixes jgm/highlighting-kate#57 (again).
  • Added float parsing tests.
  • Use parsec parsers, not regex, for CStringChar and CChar.
  • Rewrote Int, Hex, Oct, CStringChar, CCHar parsers with parsec instead of regex. This speeds things up.
  • Don't include leading + in Int, Hex, Oct parsers. That gives bad results for things like i+1.

0.3 -- 2017-02-19

  • Store literal binary-encoded representations of the Syntax structure in Skylighting.Syntax.*.hs, instead of the structure itself. This works around a problem ghc has compiling modules with large structures. This indirect method produces faster compile times and avoids massive memory usage by ghc (especially in profiling builds). For background see Closes #7.
  • Types: Internals of 'WordSet' are no longer exposed.

0.2 -- 2017-02-19

  • Restore Data, Typeable, Generic instances for basic types. To do this, we remove reCompiled field from RE (API change). Instead, we have the tokenizer compile regexes the first time it encounters them, memoizing the results. Performance is not significantly worse.
  • Skylighting.Syntax.*: use string representation of the Syntax, which is then 'read', rather than including the code for the data structure directly (#7). This indirect method produces faster compile times and avoids massive memory usage by ghc (especially in profiling builds). For background see
  • Use -fprof-auto-exported for profiling builds.
  • Added benchmark for xml syntax definition parsing.
  • Patched perl.xml (improperly escaped regex) (#8). This fixes a perl regex compilation error for regex patterns with backslash as delimiter, e.g. m\a.
  • Add a flag to build with system pcre (Felix Yan). -- 2017-02-03

  • Avoid depending on a PrintfArg instance for Text (#5). This isn't provided in some older versions of the text library. This change should allow the package to build on older platforms. -- 2017-01-31

  • Properly escape characters in subDynamic. This fixes a problem that caused failures with

    echo -e "s\0b\0c" | skylighting -s perl
  • More efficient rewrite of char escaping for regexes. -- 2017-01-29

  • Increase test timeout to 6s.
  • Avoid double {{}} in latex macros.
  • Fixed problem compiling Format.LaTeX on older ghc versions (7.8.3) that can't take a Text as PrintfArg. -- 2017-01-28

  • Added much more extensive testing to ensure that tokenizers don't hang or drop input.
  • Fixed some issues with line-end and fallthrough context handling.
  • Fixed a bug in WordDetect handling which caused it to drop input (#2). -- 2017-01-21

  • Optimized. Speed is now comparable to highlighting-kate and often better.
  • Added benchmarks.

0.1.1 -- 2017-01-19

  • Added breezeDark style, from breeze-dark.theme.
  • Fixed performance bug in regex application (#1). This gives a significant speedup, especially for inputs with long lines. -- 2016-12-23

  • Fixed bug in LaTeX renderer (backslash in wrong position). -- 2016-12-23

  • Initial release

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