This package provides length-indexed (sized) lists, also known as vectors.
data Vec n a where
VNil :: Vec 'Nat.Z a
(:::) :: a -> Vec n a -> Vec ('Nat.S n) a
The functions are implemented in four flavours:
naive: with explicit recursion. It's simple, constraint-less, yet slow.
pull: using Fin n -> a representation, which fuses well,
but makes some programs hard to write. And
data-family: which allows lazy pattern matching
inline: which exploits how GHC dictionary inlining works, unrolling
recursion if the size of Vec is known statically.
As best approach depends on the application, vec doesn't do any magic
transformation. Benchmark your code.
This package uses fin, i.e. not GHC.TypeLits, for indexes.
For lens or optics support see vec-lens and vec-optics packages respectively.
See Hasochism: the pleasure and pain of dependently typed haskell programming
by Sam Lindley and Conor McBride for answers to how and why.
Read APLicative Programming with Naperian Functors
by Jeremy Gibbons for (not so) different ones.
Similar packages
linear has V type,
which uses Vector from vector package as backing store.
Vec is a real GADT, but tries to provide as many useful instances (upto lens).
vector-sized
Great package using GHC.TypeLits. Current version (0.6.1.0) uses
finite-typelits and Int indexes.
sized-vector depends
on singletons package. vec isn't light on dependencies either,
but try to provide wide GHC support.
fixed-vector
sized also depends
on a singletons package. The Sized f n a type is generalisation of
linear's V for any ListLike.
clash-prelude
is a kitchen sink package, which has CLaSH.Sized.Vector module.
Also depends on singletons.
