Difference between revisions of "The Other Prelude"
From HaskellWiki
Nmessenger (talk  contribs) m (combined Functor (.) and map type decls) 
Uchchwhash (talk  contribs) (prettifying) 

Line 1:  Line 1:  
[[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. 
−  == Naming conventions == 

+  == Committee == 

−  The principal is to make the names very readable for both beginners and category theorists (if any). 

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

−  == Guidelines == 

+  == Naming Conventions == 

−  * The prelude should not contain any "projection" functions (like <hask>fst</hask> and <hask>snd</hask>. They go to the Extension module. 

+  * 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 == 

−  == Issues == 

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

−  * Should alphanumeric names be preferred over symbols when defining a class? 

−  * 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, ...)! 

−  
−  
−  == The hierarchy == 

* <hask>TheOtherPrelude</hask>  Minimalistic module. 
* <hask>TheOtherPrelude</hask>  Minimalistic module. 

* <hask>TheOtherPrelude.Extension</hask>  Convenient definitions. 
* <hask>TheOtherPrelude.Extension</hask>  Convenient definitions. 

−  == 
+  == 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 26:  
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. 
−   Both notations can be provided to allow for clarity in different situations. 

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  or should this be named 'ap'? 

−   or something even better? 

−   could this nice looking function 

−   refactor the liftM* idioms? 

−  
−  (>>) :: f a > f b > f b 

−  fa >> fb = (map (const id) fa) <*> fb 

+   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 

−   end of Functor hierarchy dilemma 

+   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 

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

Line 64:  Line 74:  
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> 
</haskell> 

−  How to use it, as it stands, 

+  == How To Use == 

−  
<haskell> 
<haskell> 

−  import Prelude ()  hide everything 

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

−  import TheOtherPrelude  get everything 

+   So we need to hide everything from the Prelude 

−  import qualified TheOtherPrelude.Monad.Kleisli as M  standard convention 

+  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 

</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''). 
−  * [[Ifthenelse]]  
+  * [[Ifthenelse]]  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 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.Extension
 Convenient definitions.
Open Issues
 Should Prelude functions use
Integer
instead ofInt
?
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
 donotation 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
implyFunctor m
(adopted by The Other Prelude).  Ifthenelse  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)