0.14 [2023.10.11]

• Drop support for GHCs older than 8.6.
• The forall function in Data.Constraint.Forall has been renamed to forall_, since a future version of GHC will make the use of forall as an identifier an error.
• Implement Data.Constraint.Forall using QuantifiedConstraints.
• Remove Lifting instances for ErrorT and ListT, which were removed in transformers-0.6.*.
• Add a c => Boring (Dict c) instance.
• Add the Data.Constraint.Char module, which contains utilities for working with KnownChar constraints. This module is only available on GHC 9.2 or later.
• Add unsafeAxiom to Data.Constraint.Unsafe.
• Add unsafeSChar, unsafeSNat, and unsafeSSymbol to Data.Constraint.Unsafe when building with base-4.18 (GHC 9.6) or later.

0.13.4 [2022.05.19]

• Correct the CPP introduced in constraints-0.13.3 such that it works when building with mtl-2.3.* or later combined with transformers < 0.6.

0.13.3 [2022.01.31]

• Allow building with transformers-0.6.* and mtl-2.3.*.

0.13.2 [2021.11.10]

• Allow building on GHC HEAD.

0.13.1 [2021.10.31]

• Allow building with GHC 9.2.

0.13 [2021.02.17]

• Data.Constraint.Symbol now reexports the GHC.TypeLits.AppendSymbol type family from recent versions of base (or, on old versions of base, it defines a backwards-compatibile version of AppendSymbol). The existing (++) type family for Data.Constraint.Symbol is now a synonym for AppendSymbol.

  This is technically a breaking change, as (++) was previously defined like so:

  type family (++) :: Symbol -> Symbol -> Symbol
  

  This meant that (++) could be partially applied. However, for compatibility with the way that AppendSymbol is defined, (++) is now defined like so:

  type m ++ n = AppendSymbol m n
  

  As a result, (++) can no longer be partially applied.

• Make the (++) type family in Data.Constraint.Symbol be infixr 5.

• Add implied :: (a => b) -> (a :- b) to Data.Constraint, which converts a quantified constraint into an entailment. This is only available when compiled with GHC 8.6 or later.

0.12 [2020.02.03]

• Relax the type signature for divideTimes:

  -dividesTimes :: (Divides a b, Divides a c) :- Divides a (b * c)
  +dividesTimes ::  Divides a b               :- Divides a (b * c)
  

• Simplify the type signature of dividesDef:

  -dividesDef :: forall a b. Divides a b :- ((a * Div b a) ~ b)
  +dividesDef :: forall a b. Divides a b :- (Mod b a ~ 0)
  

  The original type of diviesDef can be (partially) recovered by defining it in terms of the new dividesDef:

  dividesDef' :: forall a b. (1 <= a, Divides a b) :- ((a * Div b a) ~ b)
  dividesDef' = Sub $ case (dividesDef @a @b, euclideanNat @a @b) of
    (Sub Dict, Sub Dict) -> Dict
  

0.11.2 [2019.09.06]

• Depend on the type-equality compatibility library so that (:~~:) may be used when compiling this library with GHC 8.0. This avoids having to redefine (:~~:) directly in the internals of constraints itself.

0.11.1 [2019.08.27]

• Make Data.Constraint.Deferrable.UnsatisfiedConstraint a newtype.

0.11 [2019.05.10]

• Introduce a HasDict type class for types that witness evidence of constraints, such as Dict, (:-), Coercion, (:~:), (:~~:), and TypeRep.
• Generalize the types of withDict and (\\) to be polymorphic over any HasDict instance.
• Add type (⊢) = (:-).
• Fix unsafe mistakes in the statements of dividesDef and timesDiv in Data.Constraint.Nat.
• Make the implementations of Min and Max reduce on more inputs in Data.Constraint.Nat.
• Add minusNat and minusZero functions to Data.Constraint.Nat.
• Support hashable-1.3.* and semigroups-0.19.*.

0.10.1 [2018.07.02]

• Allow building with GHC 8.6.
• Add three axioms about (+) and (-) to Data.Constraint.Nat.

0.10

• Adapt to the Semigroup–Monoid Proposal (introduced in base-4.11):
  • Add a Semigroup instance for Dict
  • Add the appropriate (:=>) instances involving Semigroup, and change the Class () (Monoid a) instance to Class (Semigroup a) (Monoid a) when base is recent enough
  • Add the appropriate Lifting(2) instances involving Semigroup
• Data.Constraint.Nat now reexports the Div and Mod type families from GHC.TypeLits on base-4.11 or later
• Fix the type signature of maxCommutes
• Export the no method of Bottom
• Add NFData instances for Dict and (:-)

0.9.1

• Correct an improper use of unsafeCoerce in the internals of Data.Constraint.Nat and Data.Constraint.Symbol
• Correctly identify the mismatched types when you defer an unsatisfiable equality constraint through Data.Constraint.Deferrable
• Re-export the (:~~:) defined in base from Data.Constraint.Deferred with GHC 8.2 or later
• Add several new (:=>) instances for Bits, Identity, Const, Natural, IO, and Word.
• Modernize some existing Class and (:=>) instances to reflect the fact that Applicative is now a superclass of Monad on recent versions of base.

0.9

• Changes to Data.Constraint:
  • Add strengthen1 and strengthen2
• Changes to Data.Constraint.Deferrable:
  • Add a Deferrable () instance
  • The Deferrable (a ~ b) instance now shows the TypeReps of a and b when a type mismatch error is thrown
  • Add defer_ and deferEither_, counterparts to defer and deferEither which do not require proxy arguments
  • Enable PolyKinds. This allows the Deferrable (a ~ b) instance to be polykinded on all supported versions of GHC except 7.10, where the kinds must be * due to an old GHC bug
  • Introduce a heterogeneous equality type (:~~:), and use it to define a Deferrable (a ~~ b) instance on GHC 8.0 or later
• Changes to Data.Constraint.Forall:
  • Implement ForallF and ForallT in terms of Forall
  • Add ForallV and InstV (supporting a variable number of parameters)
  • Add a forall combinator
• Introduce Data.Constraint.Nat and Data.Constraint.Symbol, which contain utilities for working with KnownNat and KnownSymbol constraints, respectively. These modules are only available on GHC 8.0 or later.

0.8

• GHC 8 compatibility
• transformers 0.5 compatibility
• binary 0.8 compatibility
• Dropped support for GHC 7.6 in favor of a nicer Bottom representation.

0.7

• Found a nicer encoding of the initial object in the category of constraints using a nullary constraint.

0.6.1

• Remove the need for closed type families from the new Forall.

0.6

• Completely redesigned Data.Constraint.Forall. The old design is unsound and can be abused to define unsafeCoerce! The new design requires closed type families, so this module now requires GHC 7.8+

0.5.1

• Added Data.Constraint.Deferrable.

0.5

• Added Data.Constraint.Lifting.

0.4.1.3

• Acknowledge we actually need at least base 4.5

0.4.1.2

• Restore support for building on older GHCs

0.4.1.1

• Minor documentation fixes.

0.4.1

• Added mapDict and unmapDict.
• Added a lot of documentation.

0.4

• Typeable and Data. The Data instance for (:-) is a conservative approximation that avoids having to turn (:-) into a cartesian closed category. If it becomes a pain point for users, I know how to do that, and have done so in other libraries -- see hask, but I'm hesitant to bring such heavy machinery to bear and it isn't clear how to do it in a way that is compatible with those other libraries.

0.3.5

• Explicit role annotations

0.3.4.1

• Fixed build failures.
• Fixed an unused import warning on older GHCs.

0.3.4

• Added bottom