# Difference between revisions of "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 == |

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

− | == | + | == Naming Conventions == |

− | * The | + | * 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. | ||

Line 28: | Line 29: | ||

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 | ||

− | (<*>) :: f (a -> b) -> f a -> f b | + | |

− | + | -- 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. | ||

Line 65: | Line 77: | ||

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> | ||

− | < | + | == How To Use == |

+ | <haskell> | ||

+ | -- ''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 | |

− | 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

## 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.

## Committee

This project has no committee whatsoever. Haskell community discussed the issues 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.*,`mplus`

is replaced by`(++)`

) - whole English words and camelCase for functions (
*e.g.*,`orElse`

but not`fmap`

)

- descriptive symbols for functions that are naturally infix (

## The Hierarchy

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

`TheOtherPrelude`

- Minimalistic module.`TheOtherPrelude.Extension`

- Convenient definitions.

## Open Issues

- Should Prelude functions use
`Integer`

instead of`Int`

?

## 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
```

## 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
```

## 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
`Monad m`

imply`Functor m`

(adopted by*The Other Prelude*). - If-then-else - Making
`if`

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