Fulminate

Rich and composable error messages

While plain text is a sufficient medium for communicating with users (whether they be other programmers, or end-users), it lacks a versatile way of marking up parts of the text in a way that could be rendered in different ways as markdown, HTML or console text: usually, it's necessary to commit early to the output format. Fulminate fills this gap by providing a convenient representation of a message, with constructors which automatically contrast the dynamic parts of the message from the static parts.

Features

• rich representation of user-facing messages, particularly for errors
• demarcation of fixed and variable parts of a message
• provides a general-purpose Error type for immutable exception objects

Availability

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

Subsequently, Fulminate 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

Messages

A Message is a string of text which may have other Messages embedded within it. Unlike a string, though, Messages retain their structure, and references to the embedded Messages are retained, unchanged.

The simplest way to construct a Message is with the msg"" interpolator, for example:

val message = msg"this is a message"

Such a message can be embedded within another, as in,

val message2 = msg"We can see that $message."

which would represent the text, We can see that this is a message..

This exact text can be produced by calling Message's text method, but this flattens the structure of the message. Other libraries, such as Punctuation, Honeycomb and Escapade can render Messages as richer presentations of text, such as Markdown, HTML and console output, and in doing so, can highlight those parts of the Message which were embedded.

The msg"" interpolator also allows other types to be embedded, provided an MessageShow typeclass instance exists for that type. By default, that includes primitive types, Text strings and any type for which a Show typeclass instance exists, all of which will be automatically converted to Messages when they are substituted into the interpolator. While the Message that gets provided by an MessageShow instance may be essentially the same as the Text that is provided by a Show instance in most cases, MessageShow can provide additional structure to the text content, that becomes apparent when rendered as Markdown, HTML or console text.

Errors

An Error is a subclass of java.lang.Exception, not be confused with java.lang.Error, whose error message is expressed as a Message.

This will typically be subclassed with a case class whose parameters will be substituted into the message, for example:

case class SizeError(expected: Size, actual: Size)
extends Error(msg"expected a size $expected, but the actual size was $actual")

This would require an appropriate MessageShow[Size] (or a Show[Size]) instance in scope for the substitution to be acceptable.

fail

When writing macros, with a Quotes instance in scope, the fail method takes a Message and will produce a compile error showing that message.

If the compiler is running in a terminal with color capability, then color will be used to highlight embeddings in the failure message, by including ANSI escape codes in the output message.

Calling fail requires a contextual Realm in scope. A Realm does nothing more than to give a name to the scope for communication, and can be created with:

given Realm = realm"myproject"

Panic

Sometimes we need to raise exceptions which are not intended to be handled, and not even intended to be thrown, for example when a code branch is run which should be impossible to reach. The Panic class provides a standard way of handling such situation, and takes a Message parameter which should briefly explain the reason why the situation was believed to be impossible.

Should a Panic be thrown, it should represent a programming mistake: the manifestation of a misconception of impossibility on the part of the programmer.

Status

Fulminate is classified as maturescent. 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.

Fulminate is designed to be small. Its entire source code currently consists of 179 lines of code.

Building

Fulminate 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 Fulminate?".

1. Copy the sources into your own project

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

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

Contributing

Contributors to Fulminate 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 Fulminate 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

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

Name

To fulminate is to express vehement protest, while Fulminate provides the means to express protestations at errors.

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 a boiling, bubbling liquid; fulminating.

License

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