This package provides data types and classes for manipulating the ‘ConstraintKinds’ exposed by GHC in 7.4.
Contact Information
Contributions and bug reports are welcome!
Please feel free to contact me through github or on the #haskell IRC channel on irc.freenode.net.
-Edward Kmett
Changes
0.14.2 [2024.05.12]
Re-export Log2 from Data.Constraint.Nat.
Add log2Nat and log2Pow to Data.Constraint.Nat.
0.14.1 [2024.04.29]
Remove an unused dependency on the type-equality library.
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.
