# The Other Prelude

### From HaskellWiki

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-- the name has been chosen to reflect the magic of Church booleans! |
-- the name has been chosen to reflect the magic of Church booleans! |
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boolean True x _ = x |
boolean True x _ = x |
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− | boolean False _ y = x |
+ | boolean False _ y = y |

</haskell> |
</haskell> |

## Revision as of 06:16, 30 December 2006

## Contents |

## 1 Call For Contribution

This fun project, called *The Other Prelude*, is a creative reconstruction of the standard Prelude. By disregarding history and compatibility, we get a clean sheet.

## 2 Committee

This project has no committee whatsoever. Haskell community discussed the issues here.

## 3 Naming Conventions

- Function names should be easy for beginners to consume.
- Specifically,
*The Other Prelude*naming convention is to use- descriptive symbols for functions that are naturally infix (
*e.g.*,is replaced bymplus)(++) - whole English words and camelCase for functions (
*e.g.*,but notorElse)fmap

- descriptive symbols for functions that are naturally infix (

## 4 The Hierarchy

Although, not Haskell 98, hierarchical modules will definitely be in Haskell'. We take it for granted.

- - Minimalistic module.TheOtherPrelude
- - Convenient definitions. The reasoning behind its existence is that we want the Prelude to be very concise. It should not steal good names.TheOtherPrelude.Utilities

## 5 Open Issues

- Should Prelude functions use instead ofInteger?Int
- Should be a class rather than a type synonym?String

## 6 The Code

Currently, the code is in Wiki form. If people do agree that the collaborative decisions begot something pretty, we'll have a group of files in darcs.haskell.org some time.

The imaginery Prelude as it stands,

### 6.1 TheOtherPrelude

TheOtherPrelude

-- module: TheOtherPrelude import Prelude () -- hide everything -- the idea is to remove 'fmap'. -- both map :: (a -> b) -> [a] -> [b] ('fmap' for the monad []) -- and (.) :: (a -> b) -> (e -> a) -> (e -> b) ('fmap' for the (->) e monad) -- are good names, and are intuitively prefix and infix respectively. class Functor f where -- 'fmap' is guilty of nothing but a bad name map, (.) :: (a -> b) -> f a -> f b -- implementing either is enough map = (.) (.) = map -- the following has been shamelessly copied, -- from the [[Functor hierarchy proposal]] wiki page. class Functor f => Applicative f where -- lifting a value return :: a -> f a -- should this be named 'ap'? is 'ap' a good name? -- can you come up with a better name? -- can it refactor the liftM* type gymnastics? (<*>) :: f (a -> b) -> f a -> f b -- this leaves little left for the actual Monad class class (Applicative m) => Monad m where -- the binding operation, gist of a monad (>>=) :: m a -> (a -> m b) -> m b -- throwing out the outer monad join :: m (m a) -> m a -- when the second is independent of the first -- included in the class in case performance can be enhanced (>>) :: m a -> m b -> m b -- intuitive definitions fa >> fb = (map (const id) fa) <*> fb -- is there a better definition? x >>= f = join (map f x) join x = x >>= id -- we shamelessly copy from the [[MonadPlus reform proposal]] now. -- zero will be used when pattern matching against refutable patterns in -- do-notation as well as to provide support for monad comprehensions. -- should satisfy 'left zero': zero >>= f = zero class (Monad m) => MonadZero m where zero :: m a -- should satisfy 'monoid' -- zero ++ b = b, b ++ zero = b, (a ++ b) ++ c = a ++ (b ++ c) -- and 'left distribution' -- (a ++ b) >>= f = (a >>= f) ++ (b >>= f) class (MonadZero m) => MonadPlus m where (++) :: m a -> m a -> m a -- should satisfy 'monoid' -- zero `orElse` b = b, b `orElse` zero = b -- (a `orElse` b) `orElse` c = a `orElse` (b `orElse` c) -- and 'left catch' -- (return a) `orElse` b = a class (MonadZero m) => MonadOr m where orElse :: m a -> m a -> m a

### 6.2 TheOtherPrelude.Utilities

TheOtherPrelude.Utilities

-- module: TheOtherPrelude.Utilities import Prelude () -- hide everything -- this is the if-then-else proposal -- the name has been chosen to reflect the magic of Church booleans! boolean True x _ = x boolean False _ y = y

## 7 How To Use

-- ''The Other Prelude'' is an alternative, not a replacement. -- So we need to hide everything from the Prelude import Prelude () -- This is just an example assuming there is nothing to hide import TheOtherPrelude -- Hopefully, this module will contain lift,... -- Standard convention is to use M.lift (instead of liftM) import qualified TheOtherPrelude.Monad.Kleisli as M

## 8 See also

- Mathematical prelude discussion - A numeric Prelude in good shape already. Will a merger be ever possible?
- Prelude extensions and Prelude function suggestions - Unlike
*The Other Prelude*they*enhance*the Prelude. - Functor hierarchy proposal - Making implyMonad m(adopted byFunctor m
*The Other Prelude*). - If-then-else - Making a function (partially adopted byif
*The Other Prelude*, we are silent on the bigger issue of sugar). - MissingH - Functions "missing" from the Haskell Prelude/libraries.
- MonadPlus reform proposal - Clarifies ambiguities around MonadPlus laws (adopted by
*The Other Prelude*)