Symbolism

A general mechanism to implement overloaded symbolic operators

Many projects will find it useful to be able to define symbolic operators as extension methods for a variety of different types. Unfortunately, such methods do not always coexist happily, and overload resolution between different—but like-named—extension methods do not happily coexist in the same project: the compiler is often unable to disambiguate between different methods. Contextual resolution is, however, much more reliable, so Symbolism provides a single definition of each of the arithmetic and comparison operators, which defers their implementation to typeclasses inferred from their parameter types.

Features

• uses typeclasses as a modular way to implement symbolic operators
• avoids overloading errors when mixing different projects which define symbolic extension methods
• provides typeclasses for the arithmetic operators, +, -, * and /
• provides a single inequality typeclass for the comparison operators, <, <=, > and >=

Availability

Symbolism 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 Symbolism.

Getting Started

Using Symbolic Operators

A project which defines symbolic operator implementations using Symbolism will need Symbolism's extension methods in scope. This is simply a matter of importing it, like so:

import symbolism.*

Subsequently, any object which does not define its own +, -, *, /, <, >, <= or >= method will use Symbolism's definition, and search for an appropriate contextual instance for the implementation, based on the types of the left and right operands.

For example, calling a + b will search for an instance of Operator["+", a.type, b.type], say plus, and invoke its apply method on the parameters, a and b. The result of plus(a, b) will be plus.Result, whatever that happens to be for the particular choice of typeclass instance.

In many cases, the types a.type, b.type and plus.Result would all be the same, as they are for adding two Ints or joining two stringlike objects, but there is flexibility for the left and right operand types to be different, and for the result type to be different again.

In fact, the typeclass definitions allow for implementations to be provided with metaprogramming, which allows the result type to be computed as a function of the left and right operand types.

Implementing Symbolism's Typeclasses

Every binary operator is implemented with the Operator typeclass, or its simplified subtype, ClosedOperator (for the cases where the left, right and result types are the same). Both are parameterized on the singleton string type of the operator name, and can be used to represent any binary operator, though extension methods are (for now) only provided for +, -, * and /.

Any implementation of Operator should define the two operand types and a Result type member, which will be the type of the result of the binary operation, as well as the implementation of the operator, as its two-parameter apply method.

The apply method, and its parameters, are inlined, so as to minimize the performance cost of deferring simple operations to a typeclass, and any implementation of Operator should do the same.

Status

Symbolism is classified as embryotic. 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.

Symbolism is designed to be small. Its entire source code currently consists of 116 lines of code.

Building

Symbolism 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 Symbolism?".

1. Copy the sources into your own project

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

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

Contributing

Contributors to Symbolism 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 Symbolism 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

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

Name

Symbolism helps work with symbolic operators

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 three of the four arithmetic operators overlaid upon each other.

License

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