Changelog for constraints-0.13

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