The Other Prelude
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Revision as of 22:03, 10 January 2007 by JohannesAhlmann (talk  contribs) (added link to NotJustMaybe)
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 notfmap
)
 descriptive symbols for functions that are naturally infix (e.g.,
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 ofInt
?  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
 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
 donotation 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
 module: TheOtherPrelude.Utilities
import Prelude ()  hide everything
 this is the ifthenelse 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
implyFunctor m
(adopted by The Other Prelude).  Ifthenelse  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)
 NotJustMaybe  Instead of writing inside a specific monad (i.e. Maybe) write functions generalized on (Monad m)=> where possible.