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.

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

cabal update
cabal install vault

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