This package provides variants of functor-like structures,
with domain types are constrained.
In particular, this package provides an abstraction for functorial
containers, which can be expressed as a functor from a full-subcategory
of Hask to Hask itself [^1].

For example:

We can treat Set as if it is a Fuctor, Foldable, Applicative,
with their domain restricted to full-subcategory Ord of Ord instances
of Hask.

For MonoFoldable or MonoTraversable types (from mono-traversable package),
we provide WrapMono wrapper with zero-cost coercion. Such monos can be
regarded as a functorial structure from the full subcategory consisting of just a single object,
say Element mono.

[^1]: Strictly speaking, CFoldable, a constrained counterpart of Foldable, doesn’t require a functoriality as with the original Foldable.

Optimisation

This library is designed to keep the abstraction runtime overhead as minimum as possible.

Some notes:

If a constrained term such as cmap or czipWith has concrete type, it must have exactly the same representation as the corresponding operation modulo (zero-cost) coercion.

The same still holds if the set of required constraints coincides.

Although the constructor of WrapMono mono a is hidden, its just a newtype-wrapper around mono;
hence, constrained operators must have the same representations as the corresponding combinators
in mono-traversable package.

OTOH, for a polymorphic term, like cmap :: (Ord a, Ord b) => (a -> b) Set a -> Set b
and Set.map, they can have different representations; indeed, Set.map doesn’t require a to be Ord-instance and therefore the implementation of cmap discards the dictionary for Ord a to call Set.map.

Changes

Changelog for subcategories

0.2.1.0

Supports GHC 9.8

Drops support for GHC <9

0.2.0.1

Supports GHC 9.6

0.2.0.0

Supports GHC >= 9.2.

As base >= 4.16 removes Data.Semigroup.Option, this package
drops instance for Option accordingly for GHC >= 9.2.
It seems that PVP demands us to bump the major version.