Scrapbook-0.4.0: code examples

Copyright	© Frank Jung 2020
License	GPL-3
Safe Haskell	Safe-Inferred
Language	Haskell2010

Cps

Contents

Types
Custom continuation passing style (CPS)
CPS Function Examples

Description

Example from Wikibooks Continuation Passing Style

This uses the Cont Monad from the transformers package.

Using callCC is better than using return as argument it returns a suspended computation.

A function of type a -> b would become a -> (b -> r) -> r in CPS, where b -> r is the continuation.

Synopsis

newtype CPS a = CPS {
- runCPS :: forall r. (a -> r) -> r
}
toCPS :: a -> forall r. (a -> r) -> r
fromCPS :: (forall r. (a -> r) -> r) -> a
addCont :: Int -> Int -> Cont r Int
addOne :: Int -> Int
pythagorasCont :: Int -> Int -> Cont r Int
releaseString :: String
releaseStringCPS :: CPS String
squareCont :: Int -> Cont r Int
withOS :: (String -> r) -> r
withTimestamp :: (Int -> r) -> r
withVersionNumber :: (Double -> r) -> r

Types

newtype CPS a Source #

Type CPS for Continuation-passing style.

See CpsSpec.hs for usage.

Constructors

CPS
Fields runCPS :: forall r. (a -> r) -> r

Instances

Instances details

Applicative CPS Source #	Application instance for `CPS`.
Instance details Defined in Cps Methods pure :: a -> CPS a # (<>) :: CPS (a -> b) -> CPS a -> CPS b # liftA2 :: (a -> b -> c) -> CPS a -> CPS b -> CPS c # (>) :: CPS a -> CPS b -> CPS b # (<*) :: CPS a -> CPS b -> CPS a #
Functor CPS Source #	Functor instance for `CPS`.
Instance details Defined in Cps Methods fmap :: (a -> b) -> CPS a -> CPS b # (<$) :: a -> CPS b -> CPS a #
Monad CPS Source #	Monad instance for `CPS`.
Instance details Defined in Cps Methods (>>=) :: CPS a -> (a -> CPS b) -> CPS b # (>>) :: CPS a -> CPS b -> CPS b # return :: a -> CPS a #

Custom continuation passing style (CPS)

toCPS :: a -> forall r. (a -> r) -> r Source #

Custom continuation passing style.

The following example uses a custom continuation-passing style (CPS) to demonstrate the general concept.

This converts any value into a suspended computation.

flip ($) :: b -> (b -> c) -> c

Longhand this is: toCPS a = k -> k a

Or more simply as: toCPS a k = k a

fromCPS :: (forall r. (a -> r) -> r) -> a Source #

From custom continuation.

The following example calls the continuation function with id.

Passing id to the continuation function will return the value.

($ id) :: ((a -> a) -> b) -> b

Longhand this is: fromCPS f = f id

CPS Function Examples

addCont :: Int -> Int -> Cont r Int Source #

Continuation passing style (CPS) examples.

The following uses the Cont Monad from the transformers package.

Continuation for add function.

addOne :: Int -> Int Source #

pythagorasCont :: Int -> Int -> Cont r Int Source #

Continuation for pythagoras function.

releaseString :: String Source #

Return version, timestamp and OS as pyramid of doom.

releaseStringCPS :: CPS String Source #

Return version, timestamp and OS using the CPS type.

squareCont :: Int -> Cont r Int Source #

Continuation for square function.

withOS :: (String -> r) -> r Source #

Returns (fixed) OS.

withTimestamp :: (Int -> r) -> r Source #

Returns (fixed) timestamp.

withVersionNumber :: (Double -> r) -> r Source #

Returns (fixed) version.