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
0.10.1 [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.
