Profanity

A library for realtime interactive terminal software

Profanity makes it possible to write real-time applications that interact through the terminal by converting STDIN into an event stream of keypresses.

Features

capture a TTY terminal's individual keypresses
interprets standard keys and control keys
simple interactive line editor supporting standard keypresses
simple interactive navigable menu

Availability Plan

Profanity has not yet been published. The medium-term plan is to build Profanity 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 Profanity.

Subsequently, Profanity 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.

Getting Started

Java does not provide native support for direct access to keypress events. While Standard input (STDIN) is accessible as an input stream, it is buffered until a newline is sent, which makes it impossible for a Scala application to respond immediately to a keypress event, unless that keypress is the Enter key.

Profanity uses the Java Native Interface (JNI) to turn off buffering so that each keypress is received as soon as it happens.

Capturing the TTY

Before keypresses can be streamed as events, the TTY must be "captured". This is as simple as,

Tty.capture {
  // TTY operations are available here
}

but may not always succeed, for example if the JVM is not running inside a TTY, or if the TTY has already been captured, or if the JNI calls fail for another reason. These exceptions are checked.

Streaming keypresses

Within a Tty.capture block, a contextual Tty instance is made available, and Tty.stream can be called which will, by default, return a LazyList[Keypress], where Keypress is Profanity's standard representation of a keypress event. Keypress is an enumeration providing the following cases:

Printable(c: Char), a keypress of a printable character, for example, Shift+T is Printable('T')
Function(i: Int), a function key keypress, where i is the function key number, for example F2 is Function(2)
Ctrl(c: Char), a key combination of Ctrl and another character, for example, Ctrl+C is Ctrl('c')
a keypress of one of the following keys: Enter, Escape, Tab, Backspace, Delete, PageUp, PageDown, LeftArrow, RightArrow, UpArrow, DownArrow, CtrlLeftArrow, CtrlRightArrow, CtrlUpArrow, CtrlDownArrow, End, Home, Insert
Escape(bytes: Byte*), any other escape sequence that hasn't been identified as one of the above

Additionally, the Resize(rows: Int, cols: Int) case represents the escape sequence that reports the width and height of the console, and may be triggered by calling the Tty.reportSize(), or when a SIGWINCH event occurs, i.e. when the terminal window's size changes. So a Resize event can be handled just like a keypress event, where an action make be taken to ignore the event or redraw the screen, or something else.

Alternative keyboards

Tty.stream takes an optional type parameter, K, which determines the type used to represent keypress events, by resolving a contextual Keyboard[K] instance that interprets the bytes arriving in STDIN (either individually, or as short sequences) as instances of K.

By default, only a single Keyboard given instance is defined, parameterized on the event type, Keypress, which means that Tty.stream may be invoked without specifying its type parameter. Nevertheless, it is possible to define alternative interpreters for the byte input to STDIN.

Line Editor

Profanity provides a simple line editor that may be used inside a Tty.capture block, and will handle common keypresses that may be used inside an editable field, including printable characters, arrow keys, Ctrl key combinations such as Ctrl+W (delete word) and Ctrl+U (delete line).

This can be invoked inside a Tty.capture block with LineEditor.ask(), or pre-filled with an initial value, LineEditor.ask("initial").

Rendering

It is also possible to control how the line editor displays the text by overriding the default render method of LineEditor.ask. This parameter is a String => String lambda, mapping from the current value (i.e. the accumulation of several keypresses into a string) to the value that should be printed.

While render would normally use the identity function, it is possible to use the LineEditor.concealed method to display each character as an * or even to include ANSI escape characters (e.g. from Escapade) in the string. It is executed, and the line is redrawn, for every keypress.

Menus

A simple menu of two or more options is provided through the SelectMenu object. Its ask method, which can only be called inside a Tty.capture block, will present a set of options to the user, of which exactly one must be chosen using the arrow keys and the Enter key. In addition to the list of choices being supplied as the first parameter of SelectMenu.ask, the initially-selected value may be provided as the second.

Additionally, two lambdas, renderOn and renderOff, allow the rendering of each menu item (whether on or off) to be specified.

Limitations

Profanity does not currently support Windows.

Status

Profanity 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.

Profanity is designed to be small. Its entire source code currently consists of 364 lines of code.

Building

Profanity 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 Profanity?".

Copy the sources into your own project

Read the fury file in the repository root to understand Profanity'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.
Build with Wrath

Wrath is a bootstrapping script for building Profanity 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 profanity. Run wrath -F in the repository root. This will download and compile the latest version of Scala, as well as all of Profanity's dependencies.

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

Contributing

Contributors to Profanity 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 Profanity 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

Profanity 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 profanity is an expletive or curse-word, and Profanity imitates many of the features of the popular terminal library, Curses.

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 horns of a devil; the epitome of the profane.

propensive/profanity