vec: Vec: length-indexed (sized) list

[ bsd3, data, dependent-types, library ] [ Propose Tags ]

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:

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.

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Versions [faq] 0, 0.1, 0.1.1,, 0.2, 0.3
Change log
Dependencies adjunctions (==4.4.*), base (>=4.7 && <4.14), deepseq (>= && <1.5), distributive (>=0.5.3 && <0.7), fin (>=0.1.1 && <0.2), hashable (>= && <1.4), QuickCheck (>=2.13.2 && <2.14), semigroupoids (>=5.2.2 && <5.4), semigroups (>=0.18.4 && <0.20), transformers (>= && <0.6), transformers-compat (>=0.6.5 && <0.7) [details]
License BSD-3-Clause
Copyright (c) 2017-2019 Oleg Grenrus
Author Oleg Grenrus <>
Maintainer Oleg.Grenrus <>
Category Data, Dependent Types
Home page
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Source repo head: git clone
Uploaded by phadej at Fri Dec 13 13:44:30 UTC 2019
Distributions LTSHaskell:0.1.1, NixOS:0.3, Stackage:0.1.1
Downloads 1840 total (193 in the last 30 days)
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Status Hackage Matrix CI
Docs available [build log]
Last success reported on 2019-12-13 [all 1 reports]


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Depend on distributive to provide its instances. Turning on, disables adjunctions too.


Depend on semigroupoids to provide its instances, and traverse1.


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