Harlequin

Syntax highlighting for Scala code

Scala source code is nontrivial to parse, and while many syntax-highlighting scripts or configurations exist (for example, for editors), the complexity of the Scala language means that they can make mistakes when encountering unusual combinations of tokens. Harlequin uses the actual Scala compiler to ensure that code is parsed exactly as it would be during compilation.

The result of parsing code contains only three different types of token—spaces, newlines and content—which lend themselves to conversion to HTML or another format.

Features

• Parses fragments of Scala code using the Scala compiler
• Takes a string and returns a List of simple tokens
• Tokens represent newlines, spaces and content, for easy transformation into other formats, like HTML
• Content includes metadata to indicate its nature
• Erroneous content may also be parsed
• Parsing is fast; a short fragment will typically take a few milliseconds

Availability

Getting Started

Harlequin provides only a single method, ScalaSyntax.highlight, which takes a Text value and returns a List[Token], like so:

import harlequin.*, gossamer.*

val code = t"def inc(x: Int): Unit =\n  x + 1"
val tokens = ScalaSyntax.highlight(code)

The returned value, tokens, for this example will be the following List:

List(Code("def", Keyword), Space(1), Code("inc", Term), Code("(", Parens), Code("x", Term),
    Code(":", Symbol), Space(1), Code("Int", Type), Code(")", Parens), Code(":", Symbol), Space(1),
    Code("Unit", Type), Space(1), Code("=", Symbol), Newline, Space(2), Code("x", Ident), Space(1),
    Code("+", Ident), Space(1), Code("1", Number))

Here, each token is either, a space of a particular size, for example, Space(2) represents two space characters, a Newline, or a fragment of code, consisting of the text with an "accent"; an indication of the meaning of that code token.

Accents

The accent will be one of the following possible values:

• Error, an erroneous token,
• Ident, a reference to a term,
• Keyword, a non-modifier keyword,
• Modifier, a modifier keyword,
• Number, a number literal,
• Parens, parenthesis,
• String, a string literal (including interpolated strings),
• Term, a term definition,
• Type, a type definition.

Typically, these would be mapped to different colors during conversion to markup.

It is likely that as Harlequin evolves, the set of Accent values will grow.

Status

Harlequin is classified as fledgling. For reference, Soundness projects are categorized into one of the following five stability levels:

• embryonic: for experimental or demonstrative purposes only, without any guarantees of longevity
• fledgling: of proven utility, seeking contributions, but liable to significant redesigns
• maturescent: major design decisions broady settled, seeking probatory adoption and refinement
• dependable: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version 1.0.0 or later
• adamantine: proven, reliable and production-ready, with no further breaking changes ever anticipated

Projects at any stability level, even embryonic projects, can still be used, as long as caution is taken to avoid a mismatch between the project's stability level and the required stability and maintainability of your own project.

Harlequin is designed to be small. Its entire source code currently consists of 235 lines of code.

Building

Harlequin will ultimately be built by Fury, when it is published. In the meantime, two possibilities are offered, however they are acknowledged to be fragile, inadequately tested, and unsuitable for anything more than experimentation. They are provided only for the necessity of providing some answer to the question, "how can I try Harlequin?".

1. Copy the sources into your own project

   Read the fury file in the repository root to understand Harlequin's build structure, dependencies and source location; the file format should be short and quite intuitive. Copy the sources into a source directory in your own project, then repeat (recursively) for each of the dependencies.

   The sources are compiled against the latest nightly release of Scala 3. There should be no problem to compile the project together with all of its dependencies in a single compilation.

2. Build with Wrath

   Wrath is a bootstrapping script for building Harlequin and other projects in the absence of a fully-featured build tool. It is designed to read the fury file in the project directory, and produce a collection of JAR files which can be added to a classpath, by compiling the project and all of its dependencies, including the Scala compiler itself.

   Download the latest version of wrath, make it executable, and add it to your path, for example by copying it to /usr/local/bin/.

   Clone this repository inside an empty directory, so that the build can safely make clones of repositories it depends on as peers of harlequin. Run wrath -F in the repository root. This will download and compile the latest version of Scala, as well as all of Harlequin's dependencies.

   If the build was successful, the compiled JAR files can be found in the .wrath/dist directory.

Contributing

Contributors to Harlequin are welcome and encouraged. New contributors may like to look for issues marked beginner.

We suggest that all contributors read the Contributing Guide to make the process of contributing to Harlequin easier.

Please do not contact project maintainers privately with questions unless there is a good reason to keep them private. While it can be tempting to repsond to such questions, private answers cannot be shared with a wider audience, and it can result in duplication of effort.

Author

Harlequin was designed and developed by Jon Pretty, and commercial support and training on all aspects of Scala 3 is available from Propensive OÜ.

Name

A harlequin's clothes are a patchwork of bright colors, much as highlighted source code is.

In general, Soundness project names are always chosen with some rationale, however it is usually frivolous. Each name is chosen for more for its uniqueness and intrigue than its concision or catchiness, and there is no bias towards names with positive or "nice" meanings—since many of the libraries perform some quite unpleasant tasks.

Names should be English words, though many are obscure or archaic, and it should be noted how willingly English adopts foreign words. Names are generally of Greek or Latin origin, and have often arrived in English via a romance language.

Logo

The logo shows the motley pattern of a harlequin.

License

Harlequin is copyright © 2024 Jon Pretty & Propensive OÜ, and is made available under the Apache 2.0 License.