Anticipation

Seamless integration with minimalistic typeclass interfaces foreseen

Anticipation provides minimalistic typeclass interfaces to absolve end users of the need for cumbersome dependencies between unrelated projects.

Features

• minimalistic typeclass interfaces
• integration typeclasses for HTTP, HTML and CSS
• used by Honeycomb, Cataclysm and Scintillate
• avoids dependencies in either direction between typeclass users and providers

Availability

Anticipation 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 Anticipation.

Subsequently, Anticipation 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

Anticipation defines several typeclass interfaces to provide interoperability between different libraries, without requiring a hard dependency between them.

The Problem

Consider a library J which defines a JSON datatype, and a second library H which can return a different datatypes as HTTP responses. Neither library fundamentally requires the other, and users should be able to choose whether to depend on J or H or both.

But it would nevertheless be useful for users of both J and H to be able to return JSON HTTP responses. The JSON HTTP typeclass instance must depend on both J and H, which means that either,

1. the typeclass instance is defined in J, and J depends on H
2. the typeclass instance is defined in H, and H depends on J
3. a new module which depends on both J and H should be created

Options 1 and 2 require a dependency—in some direction—between J and H. And option 3 has the disadvantage that it creates another dependency for users to manage, both at the source-code and the build level.

The typeclass instance will have a type which looks something akin to Http[Json], where Json is defined in J and Http is defined in H. That furthermore precludes the possibility that the given instance could be defined in the companion objects of either of those types.

Ideally, users should be able to add both J and H (independently) to their build, and import no more than the packages of J and H, and automatically get access to the integration typeclass instance without any further work.

This is what Anticipation provides.

The Solution

The issues above can be circumvented by predefining a set of minimalistic typeclass interfaces for each integration point necessary, and having each library independently depend upon them.

As much as possible, the typeclass interfaces should not require any additional datatypes to be defined; they should depend only on types in the standard library. Whilst this may compromise the utility of these typeclasses, they are intended to be used only by the integration libraries; not by end-users.

Continuing the earlier example, the libraries J and H could both depend on Anticipation. J would then define a typeclass instance for its JSON type in its companion object, and H would define a typeclass converter from Anticipation's typeclass to its own user-facing typeclass interface in its companion object.

Consequently, users of both H and J could depend on both libraries, import both packages (and nothing more) and automatically be able to use the integration between them.

Anticipation Typeclasses

GenericCssSelection in the css module

Used primarily by Cataclysm, this allows different types to be used in CSS selectors. Implementations are provided in Honeycomb for its representations of CSS class names (honeycomb.Cls), DOM IDs (honeycomb.DomId), and HTML tags (honeycomb.TagType).

Paths, Files and Directories in the file module

Six typeclass interfaces provide the ability to read and write representations of paths, files and directories. These are used by projects such as Surveillance, Oubliette, Rudiments, Imperial and Guillotine to support interaction with any library which provides path-like types. Galilei provides instances for its galilei.Path, galilei.File and galilei.Directory types, and Diuretic provides instances for types in the Java standard library, such as java.io.File and java.nio.file.Path.

The typeclasses are called,

• GenericPathReader
• GenericFileReader
• GenericDirectoryReader
• GenericPathMaker
• GenericFileMaker
• GenericDirectoryMaker

In a later version of Anticipation, each Reader and Maker pair may be combined into a single typeclass.

GenericHtmlAttribute in the html module

An HTML library, most notably Honeycomb, can support attributes having typed values (rather than just strings), provided that type is suitable for the given attribute. The GenericHtmlAttribute typeclass, parameterised on the singleton literal type of the attribute name, and the value type, allows libraries to make their types usable in such HTML libraries. Gesticulate makes gesticulate.MediaTypes usable for formenctype, enctype, media and type attributes. Scintillate allows scintillate.RequestParam instances to be used for the name parameter of inputs in a form. Cataclysm supports cataclysm.CssStyle values to be used on an HTML tag's style attribute. And Serpentine and Telekinesis allow serpentine.Relative, serpentine.GenericPath, telekinesis.HttpMethod and telekinesis.Url instances to be used in the variety of attributes which support these types, such as src.

GenericHttpResponseStream and GenericHttpReader in the http module

These typeclasses provide support for working with various types over HTTP. Any type which can be streamed to HTTP, including an appropriate media type, can be furnished with a GenericHttpResponseStream instance. Libraries which provide these types include:

• Caesura, for caesura.Csv and caesura.Tsv types
• Cataclysm, for cataclysm.CssStylesheets
• Honeycomb, for honeycomb.HtmlDocs
• Jacinta, for Json values
• Xylophone, for Xml values

A GenericHttpReader instance is provided in Jacinta for reading a Json value directly from an HTTP response.

GenericInstant and GenericDuration in the time module

Any library which needs to work with time values, as instantaneous points in time or as time durations, should use GenericInstant or GenericDuration respectively. Parasite and Turbulence use these typeclasses for generic time-related operations, and instances are provided for Java types in Diuretic and Aviation for aviation.Instant and aviation.Duration types.

GenericUrl in the url module

Many libraries need to work with URLs, and the GenericUrl provides a generic interface that's use by Tarantula and Telekinesis. Diuretic provides instances for java.net.URL and Telekinesis provides an instance for its own telekinesis.Url type.

Status

Anticipation 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.

Anticipation is designed to be small. Its entire source code currently consists of 394 lines of code.

Building

Anticipation 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 Anticipation?".

1. Copy the sources into your own project

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

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

Contributing

Contributors to Anticipation 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 Anticipation 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

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

Name

Anticipation is the consideration of something before it happens, and Anticipation provides typeclass definitions in expectation of their future implementation.

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 simple floral pattern.

License

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