Cat: C++20 functional library

What is cat?

Cat is a C++20 functional library inspired by category theory and Haskell language. The purpose of cat is to provide utility functions and type classes to enable the functional programming paradigm in C++.

Rationale

The purpose of Cat library is twofold:

• to provide utility classes and functions that enable the functional programming paradigm in C++.
• to implement an extensible framework of type classes to attain a better reusability of code through the principles of category theory.

Features

The Cat library:

• is lightweight. Each function and object shipped with the library takes advantage of modern C++ features, such as constexpr constructs, movability, perfect forwarding, etc.

• is written in portable C++20 without macro black-magic, whereas template meta-programming is restricted only to the mechanics of type traits.

• implements type traits tailored for generic and functional programming (e.g. is_container, is_associative_container, function_type, function_arity, return_type, is_callable to mention a few).

• provides utilities, like callable wrappers, which enable functional composition and currying on-top-of any kind of callable types (including std::bind expressions and generic lambdas).

• provides functions that operate on std::tuple and generic containers.

• provides utilities that enable perfect forwarding from L/R value containers by means of forward_as and forward_iterator.

• includes an extensible framework for building type classes and provides the implementation of the following ones:

  • Functor
  • Bifunctor
  • Applicative
  • Alternative
  • Monoid
  • Monad
  • MonadPlus
  • Foldable
  • Show
  • Read
  • ...

• includes instances of standard C++20 and Technical Specification (TS) containers/types for the above-mentioned type classes.

Notes

At the present moment the Cat library is tested under Linux and MacOS with both glibcxx and libc++ library and with the following compilers:

• clang 14.0
• clang 6.0

Acknowledgements

The Cat library takes inspiration from the following projects:

• The Haskell language
• Fit library by Paul Fultz II
• FTL library by Bjorn Aili