semialign

Align and Zip type-classes from the common Semialign ancestor.

LTS Haskell 17.0:	1.1.0.1
Stackage Nightly 2021-01-26:	1.1.0.1
Latest on Hackage:	1.1.0.1

See all snapshots semialign appears in

BSD-3-Clause licensed by C. McCann, Oleg Grenrus

Maintained by Oleg Grenrus

This version can be pinned in stack with:semialign-1.1.0.1@sha256:44fa0af083af848efef9ac5c6cfa0d3a26fcb58d209942fae2ff941bf0f8cbe7,2444

Module documentation for 1.1.0.1

Data

Depends on 9 packages(full list with versions):

containers, hashable, semigroupoids, tagged, these, transformers, unordered-containers, vector

Used by 4 packages in nightly-2020-11-23(full list with versions):

cabal-plan, semialign-indexed, semialign-optics, subcategories

The major use of These of this is provided by the align member of Semialign class, representing a generalized notion of "zipping with padding" that combines structures without truncating to the size of the smaller input.

It turns out that zip operation fits well the Semialign class, forming lattice-like structure.

Changes

1.1.0.1

Drop base-compat dependency

1.1

Split Semialign into Semialign and Zip.
Rename old Zip into Repeat
i.e. current main hierarchy is
Remove malign, use salign or alignWith mappend where Monoid is necessary.
Add Option instances

instance Functor f => Semialign f where
    alignWith :: (These a b -> c) -> f a -> f b -> f c

instance Semialign f => Align f where
    nil :: f a

instance Semialign f => Zip f where
    zipWith :: (a -> b -> c) -> f a -> f b -> f c

instance Zip f => Repeat f where
    repeat :: a -> f a

This biased choice, that Semialign is a super-class of Zip is motivated by the fact that

There’s no Semialign-like class anywhere else, yet
Zip and Repeat are Apply (from semigroupoids) and Applicative with slightly more laws. I If you need only Repeat class, and your type isn’t Alingable, maybe using Applicative is enough?

1

Split out of these package.