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.Util

Contents

Reader
State
Writer
Exception
Choice
Orphan instances

Description

Some definitions for common effects.

Synopsis

data Reader a e ans = Reader {
- ask :: !(Op () a e ans)
}
reader :: a -> Eff (Reader a :* e) ans -> Eff e ans
data State a e ans = State {
- get :: !(Op () a e ans)
- put :: !(Op a () e ans)
}
state :: a -> Eff (State a :* e) ans -> Eff e ans
data Writer a e ans = Writer {
- tell :: !(Op a () e ans)
}
writer :: Monoid a => Eff (Writer a :* e) ans -> Eff e (ans, a)
data Except a e ans = Except {
- throwError :: !(forall b. Op a b e ans)
}
catchError :: Eff (Except a :* e) ans -> (a -> Eff e ans) -> Eff e ans
exceptEither :: Eff (Except a :* e) ans -> Eff e (Either a ans)
exceptMaybe :: Eff (Except a :* e) ans -> Eff e (Maybe ans)
exceptDefault :: ans -> Eff (Except a :* e) ans -> Eff e ans
data Choose e ans = Choose {
- none :: !(forall a. Op () a e ans)
- choose :: !(Op Int Int e ans)
}
chooseFirst :: Eff (Choose :* e) ans -> Eff e (Maybe ans)
chooseAll :: Eff (Choose :* e) a -> Eff e [a]

Reader

data Reader a e ans Source #

A standard reader effect for values of type a.

Constructors

Reader
Fields ask :: !(Op () a e ans) get the reader value of type `a` (as `perform ask ()`)

reader :: a -> Eff (Reader a :* e) ans -> Eff e ans Source #

A handler for a Reader effect with a value of type a.

State

data State a e ans Source #

A standard state effect of type a.

Constructors

State
Fields get :: !(Op () a e ans) Get the current state (as `perform get ()`) put :: !(Op a () e ans) Set the current state (as `perform put x`)

state :: a -> Eff (State a :* e) ans -> Eff e ans Source #

A state handler that takes an initial state of type a.

Writer

data Writer a e ans Source #

A standard writer effect of type a

Constructors

Writer
Fields tell :: !(Op a () e ans) Output a value of type `a` (as `perform tell msg`)

writer :: Monoid a => Eff (Writer a :* e) ans -> Eff e (ans, a) Source #

A standard Writer handler for any monoidal type a. Returns the final result of type ans and the appended tell arguments.

Exception

data Except a e ans Source #

A standard exception effect, throwing values of type a.

Constructors

Except
Fields throwError :: !(forall b. Op a b e ans) Throw an exception with a value of type `a` (as `perform throwError x`)

catchError :: Eff (Except a :* e) ans -> (a -> Eff e ans) -> Eff e ans Source #

Handle an exception.

exceptEither :: Eff (Except a :* e) ans -> Eff e (Either a ans) Source #

Transform an exception effect to an Either type.

exceptMaybe :: Eff (Except a :* e) ans -> Eff e (Maybe ans) Source #

Transform an exception effect to a Maybe type.

exceptDefault :: ans -> Eff (Except a :* e) ans -> Eff e ans Source #

Remove the exception effect using a default value in case an exception was thrown.

Choice

data Choose e ans Source #

Choose implements backtracking.

Constructors

Choose
Fields none :: !(forall a. Op () a e ans) @`perform none ()` indicates no result choose :: !(Op Int Int e ans) perform choose n` resumes up to n `times (returning` 1 `up to` n@)

chooseFirst :: Eff (Choose :* e) ans -> Eff e (Maybe ans) Source #

Return the first result found in a computation using choose for backtracking.

chooseAll :: Eff (Choose :* e) a -> Eff e [a] Source #

Return all possible results found in a computation using choose for backtracking

Orphan instances

Choose :? e => Alternative (Eff e) Source #
Instance details Methods empty :: Eff e a # (<\|>) :: Eff e a -> Eff e a -> Eff e a # some :: Eff e a -> Eff e [a] # many :: Eff e a -> Eff e [a] #
Choose :? e => MonadPlus (Eff e) Source #
Instance details Methods mzero :: Eff e a # mplus :: Eff e a -> Eff e a -> Eff e a #