Control.DoubleContinuations

This module describes DoubleContinuations, which are Continuations that may have succeeded or failed. Instead of just taking a single function (a -> r) -> r to execute after the computation has run, a double continuation takes two functions: one to call in case of success and one to call in case of error This allows for easy implementation of exception handling and structuring control flow in a pass/fail manner

Documentation

data DCont r e a

The double continuation. Takes two functions, one to invoke if the computation is successful, one if it errors

Constructors

DCont

Fields

• run :: (a -> r) -> (e -> r) -> r

Instances

Monad (DCont r e)

Binding a Continuation means running it, then feeding the result into f to generate a new continuation, and running that

Methods

(>>=) :: DCont r e a -> (a -> DCont r e b) -> DCont r e b

(>>) :: DCont r e a -> DCont r e b -> DCont r e b

return :: a -> DCont r e a

fail :: String -> DCont r e a

Functor (DCont r e)

via Monad/Functor laws

Methods

fmap :: (a -> b) -> DCont r e a -> DCont r e b

(<$) :: a -> DCont r e b -> DCont r e a

Applicative (DCont r e)

via Monad/Applicative laws

Methods

pure :: a -> DCont r e a

(<*>) :: DCont r e (a -> b) -> DCont r e a -> DCont r e b

(*>) :: DCont r e a -> DCont r e b -> DCont r e b

(<*) :: DCont r e a -> DCont r e b -> DCont r e a

Alternative (DCont r e)

An empty alternative just fails with an undefined error. Branching means first trying one, and in case of failure, the other

Methods

empty :: DCont r e a

(<|>) :: DCont r e a -> DCont r e a -> DCont r e a

some :: DCont r e a -> DCont r e [a]

many :: DCont r e a -> DCont r e [a]

throw

Arguments

:: e

The error to return

-> DCont r e a

Generates a continuation that always fails. For a continuation that always succeeds, see return

invoke :: DCont (Either e a) e a -> Either e a

Convenience function to run a computation and put the result into an Either (with Left being the error and Right being the success)