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https://github.com/propensive/fulminate

Rich user messages for Scala
https://github.com/propensive/fulminate

error-messages markup rich-messages scala

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Rich user messages for Scala

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# 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](https://github.com/propensive/fury) and to publish it as a source build

on [Vent](https://github.com/propensive/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](#building).



## Getting Started



### `Message`s



A `Message` is a string of text which may have other `Message`s embedded within

it. Unlike a string, though, `Message`s retain their structure, and references

to the embedded `Message`s are retained, unchanged.



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

```scala

val message = msg"this is a message"

```



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

```scala

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](https://github.com/propensive/punctuation/),

[Honeycomb](https://github.com/propensive/honeycomb/) and

[Escapade](https://github.com/propensive/escapade/) can render `Message`s 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 `Message`s

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.



### `Error`s



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:

```scala

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:

```scala

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 234 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](https://github.com/propensive/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`](https://github.com/propensive/wrath/releases/latest), 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](https://github.com/propensive/fulminate/labels/beginner).



We suggest that all contributors read the [Contributing

Guide](/contributing.md) 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](https://propensive.com/).



## 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 © 2025 Jon Pretty & Propensive OÜ, and

is made available under the [Apache 2.0 License](/license.md).