https://github.com/propensive/rudiments

A collection of basic, useful methods to complement the Scala stardard library
https://github.com/propensive/rudiments

predef scala scala-predef y-combinator

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A collection of basic, useful methods to complement the Scala stardard library

• Host: GitHub
• URL: https://github.com/propensive/rudiments
• Owner: propensive
• Created: 2020-01-13T12:27:27.000Z (almost 5 years ago)
• Default Branch: main
• Last Pushed: 2024-10-13T08:24:11.000Z (3 months ago)
• Last Synced: 2024-10-14T23:44:45.506Z (3 months ago)
• Topics: predef, scala, scala-predef, y-combinator
• Language: Scala
• Homepage: https://soundness.dev/rudiments/
• Size: 2.29 MB
• Stars: 8
• Watchers: 4
• Forks: 0
• Open Issues: 5
• Metadata Files:
  • Readme: .github/readme.md
  • Contributing: .github/contributing.md

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# Rudiments

__Rudimentary utilities for writing everyday Scala__

_Rudiments_ provides a small collection of tiny but useful utilities for everyday programming in Scala, and

could be considered an enhanced "predef".

## Features

- implementation of an easier-to-use Y-combinator method, `fix` with a recursion helper method, `recur`

- typesafe and mutation-safe reimplementations of several `String` operations

- `String` extractors for primitive types

- `unit`, `only`, `twin` and `triple` convenience methods to make some code patterns slightly more concise

- a typesafe `str""` string interpolator where all substitutions must be `String`s

## Availability

Rudiments 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 Rudiments.

Subsequently, Rudiments 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

Utilities in _Rudiments_ are mostly provided through extension methods, and importing the `rudiments` package

will bring all utility methods into scope.

### Y-Combinator

An implementation of a [Y-Combinator](https://shorturl.at/jqKOY), called `fix`, is provided, implemented using a

Scala 3 context function, which enables slightly more favorable syntax than was possible in Scala 2. This method

makes it easier to write code in a point-free style.

The `fix` method takes a type parameter (which must be explicitly specified for type inference) and a lambda as

its first parameter, to which an additional parameter should be supplied as its initial value. Crucially, in the

body of `fix`'s lambda, a call to `recur` should be used to signal recursion.

This is best illustrated with an example. Here is an implementation of a factorial function.

```scala

def factorial(n: Int): Int =

  fix[Int] { i => if i <= 0 then 1 else i*recur(i - 1) } (n)

```

This avoids the explicit definition of a private or nested helper function, which would normally be necessary

for a definition such as this.

### Primitive `String` Extractors

Extractors for all the primitive types are provided for matching on `String`s. These are defines as extensions

to the (virtual) companion objects of the primitive types, so they have the same names as the types they

extract.

Here is an example of them in use:

```scala

def parse(number: String): Boolean | Int | Double =

  number match

    case Boolean(b) => b

    case Int(i)     => i

    case Double(d)  => d

    case _          => 0

```

### Typesafe `String` operations

The extension method `String#cut` has identical semantics to `String#split`, but returns an immutable `IArray`

instead of an `Array`. Likewise, the methods `String#bytes` and `String#chars` mirror `String#getBytes` and

`String#toCharArray`, returning an `IArray[Byte]` and `IArray[Char]` respectively.

The `bytes` method currently uses the `UTF-8` in all cases, though this may change if there is sufficient

demand.

Four variants of the extension method `join` are provided on `Traversable[String]` instances, which provide the

same functionality as `mkString` (but only operating on `String`s) with one additional two-parameter version

that's specialized for natural language lists where each element is separated by a comma except the last, which

is preceded by a word such as `and` or `or`.

For example,

```scala

List("one", "two", "three").join(", ", " or maybe ")

```

will produce the string `one, two or maybe three`.

### Lightweight system property access

Many JVM system properties are available in the map, `System.getProperties` and are typically given identifiers

written in a dot-notation style, such as `user.dir`. Rudiments provides syntactic sugar for accessing these

dynamically through the `Sys` object, for example,

```scala

val pwd: Option[String] = Sys.user.dir()

```

### `unit`

Often a side-effecting expression returns a value which is not used at a particular call site, and can be

discarded. However, the expression's return type can result in type-inference choosing an undesired return type,

when `Unit` would be preferable, or a compile-time warning about discarded values may be produced.

The `unit` extension method silently discards the return value of any expression, and instead produces a `Unit`,

`()`.

### `only`

The `only` extension method applies a partial function to a value and lifts the result into an option.

For example,

```scala

val result: Option[Int] = string.only { case Int(i) => i*i }

```

### `str""` Interpolator

The `s""` interpolator takes parameters of `Any` type as substitutions, calling `String#toString` on them as

necessary. This may be considered too permissive, so `str""` is provided as a typesafe alternative that requires

every substitution to be a `String`.

### `twin` and `triple`

These two extension methods produce a two-tuple and a three-tuple (respectively) of repetitions of the value it

is applied to. This can be useful in a subsequent `map` operation.

## Status

Rudiments 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.

Rudiments is designed to be _small_. Its entire source code currently consists

of 809 lines of code.

## Building

Rudiments 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 Rudiments?".

1. *Copy the sources into your own project*

   

   Read the `fury` file in the repository root to understand Rudiments'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 Rudiments 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 `rudiments`.

   Run `wrath -F` in the repository root. This will download and compile the

   latest version of Scala, as well as all of Rudiments's dependencies.

   If the build was successful, the compiled JAR files can be found in the

   `.wrath/dist` directory.

## Contributing

Contributors to Rudiments are welcome and encouraged. New contributors may like

to look for issues marked

[beginner](https://github.com/propensive/rudiments/labels/beginner).

We suggest that all contributors read the [Contributing

Guide](/contributing.md) to make the process of contributing to Rudiments

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

Rudiments 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

The word _rudiment_ is defined as, "the principle which lies at the bottom of any development; an unfinished beginning", which is apt for a library whose purpose is to provide such common functionality that it might lie at the start of many other libraries.

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 burning sun, the basis for life in our solar system; it represents the foundational nature of Rudiments.

## License

Rudiments is copyright © 2024 Jon Pretty & Propensive OÜ, and

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