Copyright	(c) 2020 Microsoft Research; Daan Leijen; Ningning Xie
License	MIT
Maintainer	xnning@hku.hk; daan@microsoft.com
Stability	Experimental
Safe Haskell	None
Language	Haskell2010

Control.Ev.Ctl

Contents

Markers
Control monad
Unsafe primitives for Control.Ev.Eff

Description

Primitive module that implements type safe multi-prompt control. Used by the Control.Ev.Eff module to implement effect handlers.

Synopsis

data Marker a
markerEq :: Marker a -> Marker b -> Bool
data Ctl a = Pure !a
runCtl :: Ctl a -> a
prompt :: (Marker a -> Ctl a) -> Ctl a
yield :: Marker ans -> ((b -> Ctl ans) -> Ctl ans) -> Ctl b
unsafeIO :: IO a -> Ctl a
unsafePromptIORef :: a -> (Marker b -> IORef a -> Ctl b) -> Ctl b

Markers

data Marker a Source #

An abstract prompt marker

Instances

Instances details

Eq (Marker a) Source #
Instance details Defined in Control.Ev.Ctl Methods (==) :: Marker a -> Marker a -> Bool # (/=) :: Marker a -> Marker a -> Bool #
Show (Marker a) Source #
Instance details Defined in Control.Ev.Ctl Methods showsPrec :: Int -> Marker a -> ShowS # show :: Marker a -> String # showList :: [Marker a] -> ShowS #

markerEq :: Marker a -> Marker b -> Bool Source #

Compare two markers of different types for equality

Control monad

data Ctl a Source #

The Multi Prompt control monad, with existentials ans and b: where ans is the answer type, i.e. the type of the handler/prompt context, and b the result type of the operation.

Constructors

Pure !a

Pure results (only exported for use in the Control.Ev.Eff module)

Instances

Instances details

Monad Ctl Source #
Instance details Defined in Control.Ev.Ctl Methods (>>=) :: Ctl a -> (a -> Ctl b) -> Ctl b # (>>) :: Ctl a -> Ctl b -> Ctl b # return :: a -> Ctl a #
Functor Ctl Source #
Instance details Defined in Control.Ev.Ctl Methods fmap :: (a -> b) -> Ctl a -> Ctl b # (<$) :: a -> Ctl b -> Ctl a #
Applicative Ctl Source #
Instance details Defined in Control.Ev.Ctl Methods pure :: a -> Ctl a # (<>) :: Ctl (a -> b) -> Ctl a -> Ctl b # liftA2 :: (a -> b -> c) -> Ctl a -> Ctl b -> Ctl c # (>) :: Ctl a -> Ctl b -> Ctl b # (<*) :: Ctl a -> Ctl b -> Ctl a #

runCtl :: Ctl a -> a Source #

Run a control monad. This may fail with an "unhandled operation" error if there is a yield to a marker that escaped its prompt scope.

prompt :: (Marker a -> Ctl a) -> Ctl a Source #

Install a prompt with a specific prompt Marker to which one can yield. This connects creation of a marker with instantiating the prompt. The marker passed to the action argument should not escape the action (but this is not statically checked, only at runtime when yielding to it).

yield :: Marker ans -> ((b -> Ctl ans) -> Ctl ans) -> Ctl b Source #

yield m op yields to a specific marker and calls op in that context with a resumption k :: b -> Ctl ans that resumes at the original call-site with a result of type b. If the marker is no longer in the evaluation context, (i.e. it escaped outside its prompt) the yield fails with an "unhandled operation" error.

Unsafe primitives for Control.Ev.Eff

unsafeIO :: IO a -> Ctl a Source #

Unsafe IO in the Ctl monad.

unsafePromptIORef :: a -> (Marker b -> IORef a -> Ctl b) -> Ctl b Source #

Create an IORef connected to a prompt. The value of the IORef is saved and restored through resumptions.