Safe Haskell	Safe-Inferred
Language	Haskell2010

WhyNot

Synopsis

type (?) h a = CPS (Result h) ((->) h) a
class Handles (h :: Type) (op :: j -> k -> Type) where
- type Ex h op :: j
- clause :: e ~ Ex h op => op e u -> (Return (op e u) -> h -> Result h) -> h -> Result h
type family Result (h :: Type) :: Type
type family Return (opApp :: Type) :: Type
handle :: (h ? a) -> (a -> h -> Result h) -> h -> Result h
whynot :: (h `Handles` op, e ~ Ex h op) => op e u -> h ? Return (op e u)

Documentation

type (?) h a = CPS (Result h) ((->) h) a Source #

Girard's "why not?" monad parameterized by an effect handler. ((->) h) is equivalent to the Reader monad where computations have access to effect handlers. The purpose of the Handles typeclass is to keep track of the accumulated constraints imposed on h as an effect computation is evaluated. Since CPS is a control-flow monad which can lift any arbitrary effects from m (when m is a monad) we are effectively have constructed an effect routing monad which may not be able to actually perform all the effects, but nonetheless account for them in the types in the form of constraints.

class Handles (h :: Type) (op :: j -> k -> Type) where Source #

A predicate indicating that the handler type h can perform the side- effects of the action op.

Associated Types

type Ex h op :: j Source #

tbd this removes the need for a fundep

Methods

clause :: e ~ Ex h op => op e u -> (Return (op e u) -> h -> Result h) -> h -> Result h Source #

Handles an action and applies the continuation to it.

Instances

Instances details

Handles (ExceptHandler err a) Throw Source #
Instance details Defined in Demos Associated Types type Ex (ExceptHandler err a) Throw :: j Source # Methods clause :: forall (e :: j) (u :: k). e ~ Ex (ExceptHandler err a) Throw => Throw e u -> (Return (Throw e u) -> ExceptHandler err a -> Result (ExceptHandler err a)) -> ExceptHandler err a -> Result (ExceptHandler err a) Source #
Handles (StateHandler s a) Edit Source #
Instance details Defined in Demos Associated Types type Ex (StateHandler s a) Edit :: j Source # Methods clause :: forall (e :: j) (u :: k). e ~ Ex (StateHandler s a) Edit => Edit e u -> (Return (Edit e u) -> StateHandler s a -> Result (StateHandler s a)) -> StateHandler s a -> Result (StateHandler s a) Source #
Handles (StateHandler s a) Load Source #	`StateHandler` fulfills the `Load` operation.
Instance details Defined in Demos Associated Types type Ex (StateHandler s a) Load :: j Source # Methods clause :: forall (e :: j) (u :: k). e ~ Ex (StateHandler s a) Load => Load e u -> (Return (Load e u) -> StateHandler s a -> Result (StateHandler s a)) -> StateHandler s a -> Result (StateHandler s a) Source #
Handles (StateHandler s a) Save Source #	`StateHandler` also fulfills the `Save` operation.
Instance details Defined in Demos Associated Types type Ex (StateHandler s a) Save :: j Source # Methods clause :: forall (e :: j) (u :: k). e ~ Ex (StateHandler s a) Save => Save e u -> (Return (Save e u) -> StateHandler s a -> Result (StateHandler s a)) -> StateHandler s a -> Result (StateHandler s a) Source #
Handles (FStateHandler h s a) Load Source #
Instance details Defined in Demos Associated Types type Ex (FStateHandler h s a) Load :: j Source # Methods clause :: forall (e :: j) (u :: k). e ~ Ex (FStateHandler h s a) Load => Load e u -> (Return (Load e u) -> FStateHandler h s a -> Result (FStateHandler h s a)) -> FStateHandler h s a -> Result (FStateHandler h s a) Source #
Handles (FStateHandler h s a) Save Source #
Instance details Defined in Demos Associated Types type Ex (FStateHandler h s a) Save :: j Source # Methods clause :: forall (e :: j) (u :: k). e ~ Ex (FStateHandler h s a) Save => Save e u -> (Return (Save e u) -> FStateHandler h s a -> Result (FStateHandler h s a)) -> FStateHandler h s a -> Result (FStateHandler h s a) Source #
Handles (StateExceptHandler err s a) Load Source #
Instance details Defined in Demos Associated Types type Ex (StateExceptHandler err s a) Load :: j Source # Methods clause :: forall (e :: j) (u :: k). e ~ Ex (StateExceptHandler err s a) Load => Load e u -> (Return (Load e u) -> StateExceptHandler err s a -> Result (StateExceptHandler err s a)) -> StateExceptHandler err s a -> Result (StateExceptHandler err s a) Source #
Handles (StateExceptHandler err s a) Save Source #
Instance details Defined in Demos Associated Types type Ex (StateExceptHandler err s a) Save :: j Source # Methods clause :: forall (e :: j) (u :: k). e ~ Ex (StateExceptHandler err s a) Save => Save e u -> (Return (Save e u) -> StateExceptHandler err s a -> Result (StateExceptHandler err s a)) -> StateExceptHandler err s a -> Result (StateExceptHandler err s a) Source #
Handles (StateExceptHandler err s a) Throw Source #
Instance details Defined in Demos Associated Types type Ex (StateExceptHandler err s a) Throw :: j Source # Methods clause :: forall (e :: j) (u :: k). e ~ Ex (StateExceptHandler err s a) Throw => Throw e u -> (Return (Throw e u) -> StateExceptHandler err s a -> Result (StateExceptHandler err s a)) -> StateExceptHandler err s a -> Result (StateExceptHandler err s a) Source #

type family Result (h :: Type) :: Type Source #

The result of the effect.

Instances

Instances details

type Result (ExceptHandler err a) Source #
Instance details Defined in Demos type Result (ExceptHandler err a) = Either err a
type Result (StateHandler s a) Source #
Instance details Defined in Demos type Result (StateHandler s a) = (s, a)
type Result (FStateHandler h s a) Source #
Instance details Defined in Demos type Result (FStateHandler h s a) = a
type Result (StateExceptHandler err s a) Source #
Instance details Defined in Demos type Result (StateExceptHandler err s a) = (s, Either err a)

type family Return (opApp :: Type) :: Type Source #

The immediate value returned from an effect invocation.

Instances

Instances details

type Return (Edit s ()) Source #
Instance details Defined in Demos type Return (Edit s ()) = ()
type Return (Load s ()) Source #
Instance details Defined in Demos type Return (Load s ()) = s
type Return (Save s ()) Source #
Instance details Defined in Demos type Return (Save s ()) = ()
type Return (Throw err a) Source #
Instance details Defined in Demos type Return (Throw err a) = a

handle :: (h ? a) -> (a -> h -> Result h) -> h -> Result h Source #

A synonym of (#) for clarity.

whynot :: (h `Handles` op, e ~ Ex h op) => op e u -> h ? Return (op e u) Source #

Action constructor. In delimited continuations terms, this is similar to shift.