# Difference between revisions of "The Other Prelude"

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Uchchwhash (talk | contribs) m (x => y (yikes!)) |
Nmessenger (talk | contribs) (Pulled (>>) into Applicative. Performance seems less of a concern than generality, IMO, for this exercise. Or is Applicative.(>>) strictly invalid?) |
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-- module: TheOtherPrelude |
-- module: TheOtherPrelude |
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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'. |
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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, |
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− | -- from the |
+ | -- from the Functor hierarchy proposal[1] wiki page. |

class Functor f => Applicative f where |
class Functor f => Applicative f where |
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-- lifting a value |
-- lifting a value |
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(<*>) :: f (a -> b) -> f a -> f b |
(<*>) :: f (a -> b) -> f a -> f b |
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⚫ | |||

⚫ | |||

+ | |||

⚫ | |||

+ | fa >> fb = (map (const id) fa) <*> fb |
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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 |
+ | class Applicative m => Monad m where |

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

⚫ | |||

− | -- included in the class in case performance can be enhanced |
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⚫ | |||

-- intuitive definitions |
-- 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 |
+ | -- we shamelessly copy from the MonadPlus reform proposal[2] now. |

-- 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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Line 77: | Line 82: | ||

-- should satisfy 'left zero': zero >>= f = zero |
-- should satisfy 'left zero': zero >>= f = zero |
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− | class |
+ | class Monad m => MonadZero m where |

zero :: m a |
zero :: m a |
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+ | |||

-- should satisfy 'monoid' |
-- should satisfy 'monoid' |
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Line 84: | Line 90: | ||

-- and 'left distribution' |
-- and 'left distribution' |
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-- (a ++ b) >>= f = (a >>= f) ++ (b >>= f) |
-- (a ++ b) >>= f = (a >>= f) ++ (b >>= f) |
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− | class |
+ | class MonadZero m => MonadPlus m where |

(++) :: m a -> m a -> m a |
(++) :: m a -> m a -> m a |
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+ | |||

-- should satisfy 'monoid' |
-- should satisfy 'monoid' |
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Line 92: | Line 99: | ||

-- and 'left catch' |
-- and 'left catch' |
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-- (return a) `orElse` b = a |
-- (return a) `orElse` b = a |
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− | class |
+ | class MonadZero m => MonadOr m where |

orElse :: m a -> m a -> m a |
orElse :: m a -> m a -> m a |
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</haskell> |
</haskell> |
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+ | |||

+ | [1]: [[Functor hierarchy proposal]]<br /> |
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+ | [2]: [[MonadPlus reform proposal]] |
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=== <hask>TheOtherPrelude.Utilities</hask> === |
=== <hask>TheOtherPrelude.Utilities</hask> === |

## Revision as of 17:57, 2 January 2007

## 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.Utilities`

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

## Open Issues

- Should Prelude functions use
`Integer`

instead of`Int`

? - Should
`String`

be a class rather than a type synonym?

## 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,

`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[1] 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
-- when the second is independent of the first
(>>) :: m a -> m b -> m b
-- is there a better definition?
fa >> fb = (map (const id) fa) <*> fb
-- 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
-- intuitive definitions
x >>= f = join (map f x)
join x = x >>= id
-- we shamelessly copy from the MonadPlus reform proposal[2] 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
```

[1]: Functor hierarchy proposal

[2]: MonadPlus reform proposal

`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
```

## 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 (partially adopted by*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*)