Safe Haskell  None 

Language  Haskell2010 
Synopsis
 data Tactics f n r m a where
 GetInitialState :: Tactics f n r m (f ())
 HoistInterpretation :: (a > n b) > Tactics f n r m (f a > Sem r (f b))
 GetInspector :: Tactics f n r m (Inspector f)
 getInitialStateT :: forall f m r e. Sem (WithTactics e f m r) (f ())
 getInspectorT :: forall e f m r. Sem (WithTactics e f m r) (Inspector f)
 newtype Inspector f = Inspector {}
 runT :: m a > Sem (WithTactics e f m r) (Sem (e ': r) (f a))
 bindT :: (a > m b) > Sem (WithTactics e f m r) (f a > Sem (e ': r) (f b))
 pureT :: a > Tactical e m r a
 liftT :: forall m f r e a. Functor f => Sem r a > Sem (WithTactics e f m r) (f a)
 runTactics :: Functor f => f () > (forall x. f (m x) > Sem r2 (f x)) > (forall x. f x > Maybe x) > Sem (Tactics f m r2 ': r) a > Sem r a
 type Tactical e m r x = forall f. Functor f => Sem (WithTactics e f m r) (f x)
 type WithTactics e f m r = Tactics f m (e ': r) ': r
Documentation
data Tactics f n r m a where Source #
GetInitialState :: Tactics f n r m (f ())  
HoistInterpretation :: (a > n b) > Tactics f n r m (f a > Sem r (f b))  
GetInspector :: Tactics f n r m (Inspector f) 
getInitialStateT :: forall f m r e. Sem (WithTactics e f m r) (f ()) Source #
getInspectorT :: forall e f m r. Sem (WithTactics e f m r) (Inspector f) Source #
Get a natural transformation capable of potentially inspecting values
inside of f
. Binding the result of getInspectorT
produces a function that
can sometimes peek inside values returned by bindT
.
This is often useful for running callback functions that are not managed by polysemy code.
Example
We can use the result of getInspectorT
to "undo" pureT
(or any of the other
Tactical
functions):
ins <getInspectorT
fa <pureT
"hello" fb <pureT
True let a =inspect
ins fa  Just "hello" b =inspect
ins fb  Just True
A container for inspect
. See the documentation for getInspectorT
.
Inspector  

:: m a  The monadic action to lift. This is usually a parameter in your effect. 
> Sem (WithTactics e f m r) (Sem (e ': r) (f a)) 
:: (a > m b)  The monadic continuation to lift. This is usually a parameter in your effect. Continuations lifted via 
> Sem (WithTactics e f m r) (f a > Sem (e ': r) (f b)) 
liftT :: forall m f r e a. Functor f => Sem r a > Sem (WithTactics e f m r) (f a) Source #
Internal function to create firstorder interpreter combinators out of higherorder ones.
runTactics :: Functor f => f () > (forall x. f (m x) > Sem r2 (f x)) > (forall x. f x > Maybe x) > Sem (Tactics f m r2 ': r) a > Sem r a Source #
Run the Tactics
effect.
type Tactical e m r x = forall f. Functor f => Sem (WithTactics e f m r) (f x) Source #
Tactical
is an environment in which you're capable of explicitly
threading higherorder effect states. This is provided by the (internal)
effect Tactics
, which is capable of rewriting monadic actions so they run
in the correct stateful environment.
Inside a Tactical
, you're capable of running pureT
, runT
and bindT
which are the main tools for rewriting monadic stateful environments.
For example, consider trying to write an interpreter for
Resource
, whose effect is defined as:
dataResource
m a whereBracket
:: m a > (a > m ()) > (a > m b) >Resource
m b
Here we have an m a
which clearly needs to be run first, and then
subsequently call the a > m ()
and a > m b
arguments. In a Tactical
environment, we can write the threading code thusly:
Bracket
alloc dealloc use > do alloc' <runT
alloc dealloc' <bindT
dealloc use' <bindT
use
where
alloc' ::Sem
(Resource
': r) (f a1) dealloc' :: f a1 >Sem
(Resource
': r) (f ()) use' :: f a1 >Sem
(Resource
': r) (f x)
The f
type here is existential and corresponds to "whatever
state the other effects want to keep track of." f
is always
a Functor
.
alloc'
, dealloc'
and use'
are now in a form that can be
easily consumed by your interpreter. At this point, simply bind
them in the desired order and continue on your merry way.
We can see from the types of dealloc'
and use'
that since they both
consume a f a1
, they must run in the same stateful environment. This
means, for illustration, any put
s run inside the use
block will not be visible inside of the dealloc
block.
Power users may explicitly use getInitialStateT
and bindT
to construct
whatever data flow they'd like; although this is usually unnecessary.
type WithTactics e f m r = Tactics f m (e ': r) ': r Source #