# The Other Prelude

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[[Category:Proposals]] | [[Category:Proposals]] | ||

− | == Call | + | == Call For Contribution == |

− | This fun project, called | + | 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. |

− | == | + | == Committee == |

− | + | This project has no committee whatsoever. Haskell community discussed the issues [[Talk:The Other Prelude|here]]. | |

− | == | + | == 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.'', <hask>mplus</hask> is replaced by <hask>(++)</hask>) | ||

+ | ** whole English words and camelCase for functions (''e.g.'', <hask>orElse</hask> but not <hask>fmap</hask>) | ||

− | + | == The Hierarchy == | |

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

− | + | ||

− | + | ||

− | + | ||

− | + | ||

− | + | ||

* <hask>TheOtherPrelude</hask> - Minimalistic module. | * <hask>TheOtherPrelude</hask> - Minimalistic module. | ||

* <hask>TheOtherPrelude.Extension</hask> - Convenient definitions. | * <hask>TheOtherPrelude.Extension</hask> - Convenient definitions. | ||

− | == The | + | == Open Issues == |

+ | * Should Prelude functions use <hask>Integer</hask> instead of <hask>Int</hask>? | ||

+ | |||

+ | == 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. | 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. | ||

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import Prelude () -- hide everything | import Prelude () -- hide everything | ||

− | -- the idea is to remove 'fmap' | + | -- 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 | class Functor f where | ||

+ | -- 'fmap' is guilty of nothing but a bad name | ||

map, (.) :: (a -> b) -> f a -> f b | map, (.) :: (a -> b) -> f a -> f b | ||

+ | |||

+ | -- implementing either is enough | ||

map = (.) | map = (.) | ||

(.) = map | (.) = map | ||

− | -- the following has been shamelessly copied | + | -- the following has been shamelessly copied, |

− | -- from the | + | -- from the [[Functor hierarchy proposal]] wiki page. |

class Functor f => Applicative f where | class Functor f => Applicative f where | ||

+ | -- lifting a value | ||

return :: a -> f a | 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 | -- this leaves little left for the actual Monad class | ||

class (Applicative m) => Monad m where | class (Applicative m) => Monad m where | ||

+ | -- the binding operation, gist of a monad | ||

(>>=) :: m a -> (a -> m b) -> m b | (>>=) :: m a -> (a -> m b) -> m b | ||

+ | |||

+ | -- throwing out the outer monad | ||

join :: m (m a) -> m a | 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) | x >>= f = join (map f x) | ||

join x = x >>= id | join x = x >>= id | ||

− | -- | + | -- we shamelessly copy from the ''MonadPlus reform proposal'' now. |

+ | -- should satisfy 'left zero': zero >>= f = zero | ||

-- zero will be used when pattern matching against refutable patterns in | -- zero will be used when pattern matching against refutable patterns in | ||

-- do-notation as well as to provide support for monad comprehensions. | -- do-notation as well as to provide support for monad comprehensions. | ||

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zero :: m a | 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 | class (MonadZero m) => MonadPlus m where | ||

(++) :: m a -> m a -> m a | (++) :: 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 | class (MonadZero m) => MonadOr m where | ||

orElse :: m a -> m a -> m a | orElse :: m a -> m a -> m a | ||

− | |||

</haskell> | </haskell> | ||

− | How | + | == How To Use == |

− | + | ||

<haskell> | <haskell> | ||

− | import Prelude () | + | -- ''The Other Prelude'' is an alternative, not a replacement. |

− | import TheOtherPrelude -- | + | -- So we need to hide everything from the Prelude |

− | import qualified TheOtherPrelude.Monad.Kleisli as M | + | 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 | ||

</haskell> | </haskell> | ||

== See also == | == See also == | ||

− | * [[Mathematical prelude discussion]] - A numeric Prelude. | + | * [[Mathematical prelude discussion]] - A numeric Prelude in good shape already. Will a merger be ever possible? |

− | * [[Prelude extensions]] and [[Prelude function suggestions]] - Unlike | + | * [[Prelude extensions]] and [[Prelude function suggestions]] - Unlike ''The Other Prelude'' they ''enhance'' the Prelude. |

− | * [[Functor hierarchy proposal]] - | + | * [[Functor hierarchy proposal]] - Making <hask>Monad m</hask> imply <hask>Functor m</hask> (adopted by ''The Other Prelude''). |

− | * [[If-then-else]] - | + | * [[If-then-else]] - Making <hask>if</hask> a function. |

− | * [http://software.complete.org/missingh/static/doc/ MissingH] - | + | * [http://software.complete.org/missingh/static/doc/ MissingH] - Functions "missing" from the Haskell Prelude/libraries. |

− | + | * [[MonadPlus reform proposal]] - Clarifies ambiguities around MonadPlus laws (adopted by ''The Other Prelude'') | |

[[Category:Mathematics]] | [[Category:Mathematics]] | ||

[[Category:Code]] | [[Category:Code]] |

## Revision as of 13:34, 28 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.TheOtherPrelude.Extension

## 5 Open Issues

- Should Prelude functions use instead ofInteger?Int

## 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,

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. -- should satisfy 'left zero': zero >>= f = zero -- zero will be used when pattern matching against refutable patterns in -- do-notation as well as to provide support for monad comprehensions. 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

## 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.if
- MissingH - Functions "missing" from the Haskell Prelude/libraries.
- MonadPlus reform proposal - Clarifies ambiguities around MonadPlus laws (adopted by
*The Other Prelude*)