The adventure of ANSI escape codes

Escapade makes it easy to work safely with strings containing ANSI escape codes.

• provides a representation of strings containing ANSI escape codes
• support for 24-bit color, integrated with Iridescence color representations
• introduces the typechecked e"" string interpolator
• constant-time reduction to "plain" strings
• extensible support for different substitution types
• introduces "virtual" escapes with stack-based region tracking

Escapade has not yet been published. The medium-term plan is to build Escapade with Fury and to publish it as a source build on Vent. This will enable ordinary users to write and build software which depends on Escapade.

Subsequently, Escapade will also be made available as a binary in the Maven Central repository. This will enable users of other build tools to use it.

For the overeager, curious and impatient, see building.

ANSI escape codes provide a variety of features in terminal emulators for performing operations such as positioning the cursor, changing the appearance of text with styles like bold, italic and strike-through, as well as foreground and background colors.

To create an ANSI string, we use the e"" interpolator. This works like an ordinary string interpolator, allowing substitutions of stringlike values.

But substitutions may also be Escape instances, which do not insert any visible characters, but may change the appearance or style of subsequent characters. Many Escape instances are defined in the escapes object, for example, Bold, Underline and BrightRedFg.

These escapes may be used in an ANSI string, like so:

import escapes.*
val txt = e"This text is ${Bold}bold, ${Underline}underlined and ${BrightRedFg}bright red."

This introduces the bold and underline styles and the bright red color to the string, but once introduced, they continue indefinitely.

Thankfully, Escapade provides a convenient way to terminate styles introduced by ANSI escapes. If the character immediately following the escape is a recognized opening bracket ((, [, {, «, <), then the style will continue until a corresponding closing brace is found in the string, i.e. ), ], }, » or >.

For example,

e"This text is $Bold[bold], $Underline{underlined} and $BrightRedFg<bright red>."

will apply each style only to the words inside the brackets.

Plenty of choice is given over which type of brackets to use, so that a choice can (hopefully) be made which does not conflict with the real content of the string. Regions may be nested arbitrarily deep, and different bracketing styles may be used, but nested regions form a stack which must be terminated in order. So any closing bracket other than the type corresponding to the most recent opening bracket will not be given special treatment.

For example,

e"This text is $Bold[bold and $Italic{italic] text.}"

might be intending to display the final word, text, in italic but not bold. But the mismatched brackets would treat italic] text. as literal text, rendered in italic. And, in fact, the ANSI string would not compile due to the unclosed [ bracket.

While styles such as bold, italic, underline and reverse may be combined independently in a string, the situation is more complex with colors, as a new color simply replaces an old one, and it is not normally possible to restore the previous color; only to "reset" the color.

Indeed, this is what happens using the standard ANSI escapes provided in the escapes object.

But Escapade also provides stack-based tracking for colored text, so that regions may be nested, and the underlying color may be restored. This uses colors from Iridescence which may be substituted straight into an ANSI string, like so:

import iridescence.*
import colors.*
e"$Gold[gold, $Indigo[indigo, $HotPink[hot pink], indigo] $White[and] gold]"

Each substitution into an e"" string interpolator may apply a change to the existing style, represented by and tracked throughout the string as an instance of the case class, Style. Typically, these changes will specify the new state of properties such as bold, italic or the background color.

But the changes may also be a transformation of the existing style information. For example, the bold state could be flipped depending on what it was before, or the foreground color could be mixed with black to give a "faded" or "darkened" effect to the text, without changing its hue.

Any such transformation requires an object to be used as a substitution to an interpolated string to introduce it, plus a corresponding contextual Stylize instance, for example:

case class Fade(amount: Double)

given Stylize[Fade] = fade =>
  Stylize { style =>
    style.copy(fg = style.fg.hsv.shade(fade.amount).srgb)
  }

Escapade 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.

Escapade is designed to be small. Its entire source code currently consists of 558 lines of code.

Escapade 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 Escapade?".

1. Copy the sources into your own project

   Read the fury file in the repository root to understand Escapade'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 Escapade 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 escapade. Run wrath -F in the repository root. This will download and compile the latest version of Scala, as well as all of Escapade's dependencies.

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

Contributors to Escapade 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 Escapade 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.

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

An escapade is a "wild and exciting undertaking" which is "not necessarily lawful"; like the variety of escape codes that are only valid inside an ANSI terminal.

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.

The logo shows a hot-air balloon, indicative of an escapade.

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