witness

values that witness types

https://github.com/AshleyYakeley/witness#readme

LTS Haskell 24.18:	0.7
Stackage Nightly 2025-11-04:	0.7
Latest on Hackage:	0.7

See all snapshots witness appears in

BSD-2-Clause licensed by Ashley Yakeley

Maintained by <[email protected]>

This version can be pinned in stack with:witness-0.7@sha256:845d0c2ac74785824d035d38e3580fd30964eabdc6103ada08f195de3ad23a24,3520

Module documentation for 0.7

Data
- Data.PeanoNat
- Data.Type
  - Data.Type.Witness
    - Data.Type.Witness.Apply
    - Data.Type.Witness.General
    - Data.Type.Witness.Specific
      - Data.Type.Witness.Specific.All
      - Data.Type.Witness.Specific.ApplyStack
      - Data.Type.Witness.Specific.Concat
      - Data.Type.Witness.Specific.Either
      - Data.Type.Witness.Specific.Empty
      - Data.Type.Witness.Specific.FiniteAllFor
      - Data.Type.Witness.Specific.FixedList
      - Data.Type.Witness.Specific.List
        Data.Type.Witness.Specific.List.Element
        
        Data.Type.Witness.Specific.List.List
        
        Data.Type.Witness.Specific.List.Product
        
        Data.Type.Witness.Specific.List.Sum
      - Data.Type.Witness.Specific.Natural
      - Data.Type.Witness.Specific.OrderedWitnessMap
        Data.Type.Witness.Specific.OrderedWitnessMap.For
        
        Data.Type.Witness.Specific.OrderedWitnessMap.Of
      - Data.Type.Witness.Specific.Pair
      - Data.Type.Witness.Specific.PeanoNat
      - Data.Type.Witness.Specific.Single
      - Data.Type.Witness.Specific.Some
      - Data.Type.Witness.Specific.Symbol
      - Data.Type.Witness.Specific.WitnessMap
        Data.Type.Witness.Specific.WitnessMap.For
        
        Data.Type.Witness.Specific.WitnessMap.Of

Depends on 4 packages(full list with versions):

base, constraints, containers, countable

Used by 2 packages in nightly-2025-11-04(full list with versions):

monadology, open-witness

A witness is a value that witnesses some sort of constraint on some list of type variables. This library provides support for a wide variety of witness types. It also provides classes for representatives, which are values that represent types.

Changes

[0.7] - UNRELEASED

listProductSequence, matchListProduct
sequenceComposeListType
mapAllFor
fix for GHC 9.10

[0.6.2] - 2023-07-25

withAllConstraint, withSomeAllConstraint
listTypeToListM, listTypeForList, listTypeFind
fixedListLength, fixedListGenerate, Eq FixedList

[0.6.1] - 2022-09-12

new ListLength type family and associated functions
new Greater type family and associated functions
new FixedList type indexed by PeanoNat
new ListElement functions
new OrderedWitnessMapFor and OrderedWitnessMapOf types
new functions:
- someForToSome

[0.6] - 2022-05-08

reorganise modules
rename types and functions
additional functionality