# Difference between revisions of "The Other Prelude"

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[[Category:Proposals]] |
[[Category:Proposals]] |
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− | == 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]]. |
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− | The principal is to make the names very readable for both beginners and category theorists (if any). |
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− | == |
+ | == Naming Conventions == |

+ | * Function names should be easy for beginners to consume. |
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− | * The prelude should not contain any "projection" functions (like <hask>fst</hask> and <hask>snd</hask>. They go to the Extension module. |
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+ | * Specifically, ''The Other Prelude'' naming convention is to use |
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+ | ** descriptive symbols for functions that are naturally infix (''e.g.'', <hask>mplus</hask> is replaced by <hask>(++)</hask>) |
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+ | ** whole English words and camelCase for functions (''e.g.'', <hask>orElse</hask> but not <hask>fmap</hask>) |
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⚫ | |||

− | |||

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

− | * Should alphanumeric names be preferred over symbols when defining a class? |
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− | * Why do many functions in Prelude use <hask>Int</hask> instead of <hask>Integer</hask>? IMO, <hask>Integer</hask> should be THE preferred datatype for everything (examples: length, splitAt, replicate, drop, take, ...)! |
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− | |||

− | |||

⚫ | |||

* <hask>TheOtherPrelude</hask> - Minimalistic module. |
* <hask>TheOtherPrelude</hask> - Minimalistic module. |
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* <hask>TheOtherPrelude.Extension</hask> - Convenient definitions. |
* <hask>TheOtherPrelude.Extension</hask> - Convenient definitions. |
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− | == |
+ | == Open Issues == |

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

⚫ | |||

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 |
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− | -- 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. |
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− | -- special case from the Functor instance for ((->) e) |
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− | -- Both notations can be provided to allow for clarity in different situations. |
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class Functor f where |
class Functor f where |
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+ | -- 'fmap' is guilty of nothing but a bad name |
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map, (.) :: (a -> b) -> f a -> f b |
map, (.) :: (a -> b) -> f a -> f b |
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+ | |||

+ | -- implementing either is enough |
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map = (.) |
map = (.) |
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(.) = map |
(.) = map |
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− | -- 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 |
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+ | -- lifting a value |
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return :: a -> f a |
return :: a -> f a |
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⚫ | |||

⚫ | |||

− | -- could this nice looking function |
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− | -- refactor the liftM* idioms? |
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⚫ | |||

⚫ | |||

⚫ | |||

+ | -- should this be named 'ap'? is 'ap' a good name? |
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+ | -- can you come up with a better name? |
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+ | -- can it refactor the liftM* type gymnastics? |
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⚫ | |||

⚫ | |||

-- this leaves little left for the actual Monad class |
-- this leaves little left for the actual Monad class |
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class (Applicative m) => Monad m where |
class (Applicative m) => Monad m where |
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+ | -- the binding operation, gist of a monad |
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(>>=) :: m a -> (a -> m b) -> m b |
(>>=) :: m a -> (a -> m b) -> m b |
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+ | |||

+ | -- throwing out the outer monad |
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join :: m (m a) -> m a |
join :: m (m a) -> m a |
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+ | |||

− | |||

+ | -- when the second is independent of the first |
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+ | -- included in the class in case performance can be enhanced |
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⚫ | |||

+ | |||

+ | -- intuitive definitions |
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⚫ | |||

x >>= f = join (map f x) |
x >>= f = join (map f x) |
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join x = x >>= id |
join x = x >>= id |
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+ | -- we shamelessly copy from the ''MonadPlus reform proposal'' now. |
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− | -- end of Functor hierarchy dilemma |
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+ | -- should satisfy 'left zero': zero >>= f = zero |
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-- zero will be used when pattern matching against refutable patterns in |
-- zero will be used when pattern matching against refutable patterns in |
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-- 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 |
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+ | -- should satisfy 'monoid' |
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+ | -- zero ++ b = b, b ++ zero = b, (a ++ b) ++ c = a ++ (b ++ c) |
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+ | -- and 'left distribution' |
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+ | -- (a ++ b) >>= f = (a >>= f) ++ (b >>= f) |
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class (MonadZero m) => MonadPlus m where |
class (MonadZero m) => MonadPlus m where |
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(++) :: m a -> m a -> m a |
(++) :: m a -> m a -> m a |
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+ | -- should satisfy 'monoid' |
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+ | -- zero `orElse` b = b, b `orElse` zero = b |
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+ | -- (a `orElse` b) `orElse` c = a `orElse` (b `orElse` c) |
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+ | -- and 'left catch' |
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+ | -- (return a) `orElse` b = a |
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class (MonadZero m) => MonadOr m where |
class (MonadZero m) => MonadOr m where |
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orElse :: m a -> m a -> m a |
orElse :: m a -> m a -> m a |
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− | |||

</haskell> |
</haskell> |
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+ | == How To Use == |
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− | How to use it, as it stands, |
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− | |||

<haskell> |
<haskell> |
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+ | -- ''The Other Prelude'' is an alternative, not a replacement. |
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⚫ | |||

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

⚫ | |||

+ | |||

+ | -- This is just an example assuming there is nothing to hide |
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⚫ | |||

+ | |||

+ | -- Hopefully, this module will contain lift,... |
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+ | -- Standard convention is to use M.lift (instead of liftM) |
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⚫ | |||

</haskell> |
</haskell> |
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== See also == |
== See also == |
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− | * [[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'') |
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− | |||

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

## Revision as of 13:34, 28 December 2006

## 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*)