21gramconsulting/invertible

Summary

A TypeScript library to allow you to implement strict, strongly typed,invertible (a.k.a. reversible) functions and pipelines (a.k.a. compositions) of pure functions.

Common Use Cases

• Transalation: Commit-Rollback-style translating between two different types of objects, e.g. between a database model and a domain model.
• Undo/Redo GUI Features
• Serialization/Deserialization: e.g. JSON <-> TypeScript objects
• Encryption/Decryption
• CLI Programs: Typically you want both pipelines and invertible functions in CLI programs. Pipelines are useful for composing together a series of pure functions to implement the program's logic. Invertible functions are useful for implementing CLI flags that can be used to modify the program's behavior.

Terminology

• Proverse: A function that takes a value of type A and returns a value of type B.
• Inverse: A function defined with its Proverse pair in context, that takes a value of type B and returns a value of type A. Therefore, all Inverse functions are also Proverse functions, but not all Proverse functions are Inverse functions.
• Invertible: A function that has both its Proverse and Inverse defined.
• Pipeline: A composition of Proverse functions.

Potentially Unfamiliar Conventions

• Static & Runtime Parity: We at 21Gram always aim to implement runtime aspects of pure types with the same name and same or similar API that represent the very same mental model concepts. For example, you may have an IsNonEmpty type and an IsNonEmpty function for runtime use. The type resolves a true or false type to make conditional typing easier, while the function returns an item is NonEmpty boolean value at runtime.

Examples

For now, please see the tests for examples. We have full 100% coverage and this whole show is for free.