Difference between revisions of "The Other Prelude"
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CaleGibbard (talk  contribs) 
Nmessenger (talk  contribs) (Formatting, small code changes, moved method synonyms outside classes to enforce consistency (choices were arbitrary, change if you want)) 

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−  [[Category:Proposals]] 

−  
== Call For Contribution == 
== 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. 
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 == 
== Committee == 

−  This project has no committee whatsoever. Haskell community discussed the issues [[Talk:The Other Preludehere]]. 

+  
+  This project has no committee whatsoever. Issues are discussed on [[Talk:The Other Preludethe talk page]]. 

== Naming Conventions == 
== Naming Conventions == 

+  
* Function names should be easy for beginners to consume. 
* Function names should be easy for beginners to consume. 

* Specifically, ''The Other Prelude'' naming convention is to use 
* Specifically, ''The Other Prelude'' naming convention is to use 

Line 14:  Line 15:  
== The Hierarchy == 
== The Hierarchy == 

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

Line 19:  Line 21:  
== Open Issues == 
== Open Issues == 

+  
* Should <hask>Functor</hask> imply <hask>Monad</hask> or the other way around? 
* Should <hask>Functor</hask> imply <hask>Monad</hask> or the other way around? 

* When the same function has an infix and a prefix implementation, should one of them be outside the class to enforce consistency? 
* When the same function has an infix and a prefix implementation, should one of them be outside the class to enforce consistency? 

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== Reality == 
== Reality == 

+  
What we have here right now is not ready to be adopted by existing projects. May be the [[class system extension proposal]] can make a difference. 
What we have here right now is not ready to be adopted by existing projects. May be the [[class system extension proposal]] can make a difference. 

−  
== The Code == 
== 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. 

−  The 
+  The imaginary Prelude as it stands, 
−  +  
+  === <hask>TheOtherPrelude.hs</hask> === 

+  
<haskell> 
<haskell> 

−  +  module TheOtherPrelude where 

−  import Prelude ()  hide everything 

+  import Prelude ()  hide everything 

−   
+   The idea is to rename 'fmap'. 
−   
+   Both map :: (a > b) > [a] > [b] (in []) 
−   and (.) :: (a > b) > (e > a) > (e > b) ( 
+   and (.) :: (a > b) > (e > a) > (e > b) (in (>) e) 
−   are good names, and are intuitively prefix and infix respectively. 
+   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  defined outside the class as an infix synonym for map. 

−  map = (.) 

−  (.) = map 

+   The following has been shamelessly copied from the 

+   Functor hierarchy proposal page (see links below). 

+  class (Functor p) => Applicative p where 

+   Minimal complete definition: return and (<*>). 

+  return :: a > p a  value lifting 

+  (<*>) :: p (a > b) > p a > p b  lifted application 

+  (>>) :: p a > p b > p b  when the second is independent of the first 

−   the following has been shamelessly copied, 

+   Default definition: 

−   from the Functor hierarchy proposal[1] wiki page. 

−  class Functor f => Applicative f where 

−   lifting a value 

−  return :: a > f a 

−  
−   lifted application, in prefix and infix form 

−  apply, (<*>) :: f (a > b) > f a > f b 

−  
−   when the second is independent of the first 

−  (>>) :: m a > m b > m b 

−  
−  
−   implementing either is enough 

−  apply = (<*>) 

−  (<*>) = apply 

−  
−   is there a better definition? 

f >> g = (map (const id) f) <*> g 
f >> g = (map (const id) f) <*> g 

+  apply = (<*>)  defined outside the class as a prefix synonym for (<*>). 

−   this leaves little left for the actual Monad class 

+  class (Applicative m) => Monad m where 

−  class Applicative m => Monad m where 

+   Minimal complete definition: one of join or (>>=). 

(>>=) :: m a > (a > m b) > m b  bind 
(>>=) :: m a > (a > m b) > m b  bind 

−  join :: m (m a) > m a  combining levels of structure 
+  join :: m (m a) > m a  combining levels of structure 
−   Minimal complete instance: one of join or (>>=). 

 Default definitions: 
 Default definitions: 

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 (link below) now. 

−   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 

 donotation as well as to provide support for monad comprehensions. 
 donotation as well as to provide support for monad comprehensions. 

+   Should satisfy 'left zero': zero >>= f = zero 

+  class (Monad mz) => MonadZero mz where 

+  zero :: mz 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 mp) => MonadPlus mp where 

−   
+  (++) :: mp a > mp a > mp a 
−   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': 

−   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 mo) => MonadOr mo where 

−  +  orElse :: mo a > mo a > mo a 

−  orElse :: m a > m a > m a 

</haskell> 
</haskell> 

−  [1]: [[Functor hierarchy proposal]]<br /> 

+  === <hask>TheOtherPrelude/Utilities.hs</hask> === 

−  [2]: [[MonadPlus reform proposal]]<br /> 

−  [3]: [[Class system extension proposal]] 

−  === <hask>TheOtherPrelude.Utilities</hask> === 

<haskell> 
<haskell> 

−  +  module TheOtherPrelude.Utilities where 

−  
import Prelude ()  hide everything 
import Prelude ()  hide everything 

Line 117:  Line 107:  
boolean True x _ = x 
boolean True x _ = x 

boolean False _ y = y 
boolean False _ y = y 

−  
</haskell> 
</haskell> 

+  
== How To Use == 
== How To Use == 

+  
<haskell> 
<haskell> 

 ''The Other Prelude'' is an alternative, not a replacement. 
 ''The Other Prelude'' is an alternative, not a replacement. 

 So we need to hide everything from the Prelude 
 So we need to hide everything from the Prelude 

−  import Prelude () 
+  import Prelude () 
 This is just an example assuming there is nothing to hide 
 This is just an example assuming there is nothing to hide 

−  import TheOtherPrelude 
+  import TheOtherPrelude 
 Hopefully, this module will contain lift,... 
 Hopefully, this module will contain lift,... 

 Standard convention is to use M.lift (instead of liftM) 
 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 == 

+  
* [[Class system extension proposal]]  Makes this proposal worth reading at last 
* [[Class system extension proposal]]  Makes this proposal worth reading at last 

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

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

* [http://haskell.org/hawiki/NotJustMaybe NotJustMaybe]  Instead of writing inside a specific monad (i.e. Maybe) write functions generalized on (Monad m)=> where possible. 
* [http://haskell.org/hawiki/NotJustMaybe NotJustMaybe]  Instead of writing inside a specific monad (i.e. Maybe) write functions generalized on (Monad m)=> where possible. 

+  
+  [[Category:Proposals]] 

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

[[Category:Code]] 
[[Category:Code]] 
Revision as of 23:49, 19 January 2007
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. Issues are discussed on the talk page.
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
Functor
implyMonad
or the other way around?  When the same function has an infix and a prefix implementation, should one of them be outside the class to enforce consistency?
 Should Prelude functions use
Integer
instead ofInt
?  Should
String
be a class rather than a type synonym?  The current proposal lacks a well thought
fail
mechanism. Should it be integrated intoMonadZero
, or have a class of his own, or remain in theMonad
class?
Reality
What we have here right now is not ready to be adopted by existing projects. May be the class system extension proposal can make a difference.
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 imaginary Prelude as it stands,
TheOtherPrelude.hs
module TheOtherPrelude where
import Prelude ()  hide everything
 The idea is to rename 'fmap'.
 Both map :: (a > b) > [a] > [b] (in [])
 and (.) :: (a > b) > (e > a) > (e > b) (in (>) e)
 are good names, and are intuitively prefix and infix respectively.
class Functor f where
map :: (a > b) > f a > f b
(.) = map  defined outside the class as an infix synonym for map.
 The following has been shamelessly copied from the
 Functor hierarchy proposal page (see links below).
class (Functor p) => Applicative p where
 Minimal complete definition: return and (<*>).
return :: a > p a  value lifting
(<*>) :: p (a > b) > p a > p b  lifted application
(>>) :: p a > p b > p b  when the second is independent of the first
 Default definition:
f >> g = (map (const id) f) <*> g
apply = (<*>)  defined outside the class as a prefix synonym for (<*>).
class (Applicative m) => Monad m where
 Minimal complete definition: one of join or (>>=).
(>>=) :: m a > (a > m b) > m b  bind
join :: m (m a) > m a  combining levels of structure
 Default definitions:
x >>= f = join (map f x)
join x = x >>= id
 We shamelessly copy from the MonadPlus reform proposal (link below) 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 mz) => MonadZero mz where
zero :: mz 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 mp) => MonadPlus mp where
(++) :: mp a > mp a > mp 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 mo) => MonadOr mo where
orElse :: mo a > mo a > mo a
TheOtherPrelude/Utilities.hs
module TheOtherPrelude.Utilities where
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
 Class system extension proposal  Makes this proposal worth reading at last
 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)
 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.
 NotJustMaybe  Instead of writing inside a specific monad (i.e. Maybe) write functions generalized on (Monad m)=> where possible.