subcategories: Subcategories induced by class constraints

[ bsd3, data, library ] [ Propose Tags ]

Please see the README on GitHub at https://github.com/konn/subcategories#readme


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Versions [faq] 0.1.0.0
Change log ChangeLog.md
Dependencies base (>=4.7 && <5), containers, data-default, foldl, hashable, mono-traversable, pointed, primitive, reflection, semialign, template-haskell, text, these, unordered-containers, vector, vector-algorithms, vector-builder [details]
License BSD-3-Clause
Copyright 2018 (c) Hiromi ISHII
Author Hiromi ISHII
Maintainer konn.jinro _at_ gmail.com
Category Data
Home page https://github.com/konn/subcategories#readme
Bug tracker https://github.com/konn/subcategories/issues
Source repo head: git clone https://github.com/konn/subcategories
Uploaded by HiromiIshii at 2020-09-06T04:07:51Z
Distributions NixOS:0.1.0.0
Downloads 46 total (4 in the last 30 days)
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Status Hackage Matrix CI
Docs available [build log]
Last success reported on 2020-09-06 [all 1 reports]

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Readme for subcategories-0.1.0.0

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The subcategories package

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.

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.