vault

a persistent store for values of arbitrary types

https://github.com/HeinrichApfelmus/vault

LTS Haskell 24.52:	0.3.2.0
Stackage Nightly 2026-07-30:	0.3.2.0
Latest on Hackage:	0.3.2.0

See all snapshots vault appears in

BSD-3-Clause licensed by Heinrich Apfelmus, Elliott Hird

Maintained by Heinrich Apfelmus <apfelmus at quantentunnel de>

This version can be pinned in stack with:vault-0.3.2.0@sha256:ef8c56be9bdb8f657461355aa98c659a2b116b8be6447a05ffcab853990d10be,2764

Module documentation for 0.3.2.0

Data
- Data.Unique
  - Data.Unique.Really
- Data.Vault
  - Data.Vault.Lazy
  - Data.Vault.ST
    - Data.Vault.ST.Lazy
    - Data.Vault.ST.Strict
  - Data.Vault.Strict
Internal
- Internal.Data
  - Internal.Data.Vault
    - Internal.Data.Vault.ST
      - Internal.Data.Vault.ST.IORef

Depends on 4 packages(full list with versions):

base, containers, hashable, unordered-containers

Used by 17 packages in nightly-2026-07-30(full list with versions):

aws-lambda-haskell-runtime-wai, aws-xray-client-wai, bluefin-internal, hs-opentelemetry-api, hs-opentelemetry-instrumentation-persistent, hs-opentelemetry-instrumentation-wai, persistent, persistent-postgresql, reactive-banana, servant, serversession-frontend-wai, threepenny-gui, wai, wai-extra, wai-saml2, wai-session, warp

Vault is a tiny library that provides a single data structure called vault.

A vault is a type-safe, persistent storage for values of arbitrary types. Like IORef, I want to be able to store values of any type in it, but unlike IORef, I want the storage space to behave like a persistent, first-class data structure, as appropriate for a purely functional language.

It is analogous to a bank vault, where you can access different bank boxes with different keys; hence the name.

In other words, a vault is an abstract data type with the following basic signature

data Key a
data Vault

newKey :: IO (Key a)
empty  :: Vault
lookup :: Key a -> Vault -> Maybe a
insert :: Key a -> a -> Vault -> Vault
delete :: Key a -> Vault -> Vault

A few common functions for finite maps, like adjust and union, are provided as well.

This library was created thanks to the feedback on my blog post Vault - a persistent store for values of arbitrary types.

Installation

The whole thing is available on hackage, so you just have to type

cabal update
cabal install vault

Feedback

Use the issue tracker or send an email to the maintainer.

Contributors

Many thanks to…

… and others!

Changes

Changelog for the `vault` package

next version

0.3.2.0

Changed

Make value type of Key representational (in GHC backend)

Fixed

Fix potential race condition in IORef backend.

0.3.1.6

Added

Add support for MicroHs

Removed

Dropped support for GHC < 8.4

0.3.1.5

Compatibility with GHC-9.0
- Bump dependencies to allow base >= 4.5 && < 4.16
Depend on semigroups only with GHC < 8.0

0.3.1.4

Compatibility with GHC-8.10
- Bump dependencies to allow base >= 4.5 && < 4.15

0.3.1.3

Bump dependencies to allow hashable-1.3.
Compatibility with GHC-8.8
- Bump dependencies to allow base >= 4.5 && < 4.14

0.3.1.2

Bump dependencies to allow containers-0.6.
Compatibility with GHC-8.6
- Bump dependencies to allow base >= 4.5 && < 4.13.

0.3.1.1

Rename source files to allow building the package with Bazel.

0.3.1.0

Compatibility with GHC-8.4:
- Bump dependencies to allow base >= 4.5 && < 4.12.
- Add Semigroup instances.

0.3.0.7

Bump dependencies to allow base >= 4.5 && < 4.11.

0.3.0.6

Bump dependencies to allow base >= 4.5 && < 4.10.

0.3.0.5

Add support for GHC type roles extension, using the RoleAnnotations language pragma.

0.3.0.4

Bump upper version bound for the base dependency.

0.3.0.3

Bump upper version bound for the base dependency.

0.3.0.2

Fix tarball.

0.3.0.1

Use CPP to reduce code duplication.

0.3.0.0

Split modules into Lazy and Strict variants, no default choice.
Add Hashable instance to Data.Unique.Really for all implementations.