data-elevator-0.1.0.2: Coerce between unlifted boxed and lifted types.
Safe HaskellSafe-Inferred
LanguageHaskell2010

Data.Elevator

Description

Near zero-cost coercions between lifted and boxed unlifted types.

Turn any lifted type into an unlifted boxed type with Strict, eagerly forcing any wrapped computation in the syntactic binding context.

Turn any unlifted boxed type into a lifted type with Lazy, suspending any wrapped computation until the Lazy is matched upon.

Re-use existing code by coercing functions that can be generalised according to the levity polymorphism subkinding law Unlifted <: Lifted with levCoerce.

Synopsis

Documentation

type UnliftedType = TYPE UnliftedRep #

The kind of boxed, unlifted values, for example Array# or a user-defined unlifted data type, using -XUnliftedDataTypes.

type LiftedType = Type Source #

The kind of boxed, lifted types, for example [Int] or any other user-defined data type.

data Strict (a :: LiftedType) where Source #

Turn a lifted data type into an unlifted one. Unlifted data types enjoy a call-by-value calling convention. E.g.,

let f :: (a :: UnliftedType) -> Int
    f _ = 42
in f (Strict (error "boom" :: Int))

Will error out with "boom".

Note however that most function definitions don't take argument types of kind UnliftedType. Use levCoerce to work around that.

Bundled Patterns

pattern Strict :: a -> Strict a 

Instances

Instances details
LevitySubsumption (Strict a :: UnliftedType) (a :: LiftedType) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: Strict a -> a Source #

data Lazy (a :: UnliftedType) where Source #

Turn an unlifted boxed type into a lifted one. Lazy a then enjoys a call-by-name calling convention. E.g.,

let f :: a -> Int
    f _ = 42
in f (Lazy (error "boom" :: Array# Int))

Will evaluate to 42 and not error.

Bundled Patterns

pattern Lazy :: a -> Lazy a 

Instances

Instances details
LevitySubsumption (a :: UnliftedType) (Lazy a :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: a -> Lazy a Source #

levCoerce :: LevitySubsumption a b => a -> b Source #

Re-use existing code taking arguments lazily to take arguments Strictly by coercing with levCoerce.Example: even can be re-used on Strict Int:

>>> levCoerce @(Int -> Bool) @(Strict Int -> Bool) even (Strict 42)
True

More generally, any type of kind UnliftedType can act as a ("is-a") type of kind LiftedType. This levity polymorphism subkinding axiom Unlifted <: Lifted is encoded in LevitySubsumption and is lifted to useful instances for Strict, Lazy and (->). Example with covariance in the result type:

>>> levCoerce @(Int -> Strict Bool) @(Strict Int -> Bool) (\x -> Strict (even x)) (Strict 42)
True

A function from Int to Strict Bool can be called on a Strict Int (e.g., the precondition strengthened) and the result can be coerced to Bool (e.g., the postcondition weakened).

You can also keep on coercing in negative position of the function arrow, with the variance following polarity:

levCoerce @((Strict Int -> Int) -> Int)
          @((Int -> Strict Int) -> Int)
          (\f -> f (Strict 42))
          (\x -> Strict x)

class LevitySubsumption (a :: TYPE (BoxedRep l)) (b :: TYPE (BoxedRep r)) where Source #

Similar to Coercible, this type class models a subkinding relationship between two types. The instances lift the Unlifted <: Lifted sub-kinding relationship to TYPE, Strict, Lazy and then over function types.

Like for Coercible, the instances of this type class should ultimately be compiler-generated.

Methods

levCoerce# :: a -> b Source #

Instances

Instances details
LevitySubsumption (a :: LiftedType) (a :: LiftedType) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: a -> a Source #

LevitySubsumption (a :: UnliftedType) (a :: UnliftedType) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: a -> a Source #

LevitySubsumption (a :: UnliftedType) (Lazy a :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: a -> Lazy a Source #

LevitySubsumption (Strict a :: UnliftedType) (a :: LiftedType) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: Strict a -> a Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #

(LevitySubsumption a2 a1, LevitySubsumption b1 b2) => LevitySubsumption (a1 -> b1 :: Type) (a2 -> b2 :: Type) Source # 
Instance details

Defined in Data.Elevator.Internal

Methods

levCoerce# :: (a1 -> b1) -> a2 -> b2 Source #