polysemy-keyed-state: Effect for a set of stateful values indexed by a type of keys

[ bsd3, library ] [ Propose Tags ]

The KeyedState k effect provides access to a set of stateful values indexed by some key type k :: Type -> Type, where a key of type k a can be used to access a stateful value of type a.


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Versions [RSS] 0.1, 0.1.1
Change log CHANGELOG.md
Dependencies base (>=4.12 && <4.15), constraints (>=0.11 && <0.14), constraints-extras (>=0.3.0.2 && <0.4), polysemy (>=1.3 && <1.6), some (>=1.0.1 && <1.1), StateVar (>=1.2 && <1.3), trivial-constraint (>=0.3 && <0.8) [details]
License BSD-3-Clause
Author
Maintainer Katie Casamento <kcsmnt0@gmail.com>
Category BSD3, Library
Home page https://github.com/kcsmnt0/polysemy-keyed-state#readme
Bug tracker https://github.com/kcsmnt0/polysemy-keyed-state/issues
Source repo head: git clone https://github.com/kcsmnt0/polysemy-keyed-state
Uploaded by kcsmnt0 at 2021-07-13T21:54:29Z
Distributions NixOS:0.1.1
Downloads 148 total (8 in the last 30 days)
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Status Docs available [build log]
Last success reported on 2021-07-13 [all 1 reports]

Readme for polysemy-keyed-state-0.1.1

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polysemy-keyed-state

build/test

This package provides the KeyedState effect for use with polysemy. For any key type k :: Type -> Type, the KeyedState k effect provides access to a set of stateful values indexed by k, where a key of type k a can be used to access a stateful value of type a.

In the most direct use case, the KeyedState effect can be used as an interface to low-level reference types like IORef and STRef: for example, getAt can be used with the type Member (KeyedState IORef) r => IORef a -> Sem r a.

At a higher level, key types defined as GADTs can be used with KeyedState to represent sets of stateful variables in a single effect. For example, with the GADT definition of K below, the effect KeyedState K provides access to an Int value with key X and a Bool value with key Y.

data K a where
  X :: K Int
  Y :: K Bool

By mapping high-level keys to low-level references, the KeyedState effect can be used to implement a high-level interface to a set of low-level variables.

Some of the interpreters for KeyedState require instances of Has for certain typeclasses, which can be generated for most GADT key types with deriveArgDict from the constraints-extras package.