| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Polysemy.Several
Contents
Synopsis
- data HList a where
- type family TypeMap (f :: a -> b) (xs :: [a]) where ...
- type family TypeConcat (a :: [t]) (b :: [t]) where ...
- runSeveral :: (forall r' k x. k -> Sem (e k ': r') x -> Sem r' x) -> HList t -> Sem (TypeConcat (TypeMap e t) r) a -> Sem r a
Data
A list capable of storing values of different types. Like the Sem type, it uses a type level list to keep track of what's stored inside. Creating an HList looks like:
1 ::: "test" ::: True ::: HNil
type family TypeMap (f :: a -> b) (xs :: [a]) where ... Source #
A map function over type level lists. For example, the following two lines are equivalent:
TypeMap Reader [Int, String, False] [Reader Int, Reader String, Reader Bool]
type family TypeConcat (a :: [t]) (b :: [t]) where ... Source #
Like ++ but at the type level. The following two lines are equivalent:
TypeConcat [Int, String] [Bool] [Int, String, Bool]
Equations
| TypeConcat '[] b = b | |
| TypeConcat (a ': as) b = a ': TypeConcat as b |
runSeveral :: (forall r' k x. k -> Sem (e k ': r') x -> Sem r' x) -> HList t -> Sem (TypeConcat (TypeMap e t) r) a -> Sem r a Source #
A helper function for building new runners which accept HLists intsead of individual elements. If you would normally write
f 5 . f "Text" . f True
then this function can turn that into
runSeveral f (True ::: "Text" ::: 5 ::: HNil)
For example, a runReaders function could be implemented as:
runReaders :: HList t -> Sem (TypeConcat (TypeMap Reader t) r) a -> Sem r a runReaders = runSeveral runReader
Likewise, runStates could be the following if you didn't want the returned state:
runStates :: HList t -> Sem (TypeConcat (TypeMap State t) r) a -> Sem r a runStates = runSeveral (fmap (fmap snd) . runState)