# The Other Prelude

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Revision as of 21:27, 23 December 2006 by CaleGibbard (talk | contribs)

## Contents

## Call for contribution

This fun project, called "The Other Prelude", and is a creative reconstruction of the standard Prelude. By disregarding history and compatibility, we get a clean sheet.

## Naming conventions

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

## Guidelines

- The prelude should not contain any "projection" functions (like
`fst`

and`snd`

. They go to the Extension module.

## Issues

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

## The hierarchy

`TheOtherPrelude`

- Minimalistic module.`TheOtherPrelude.Extension`

- Convenient definitions.

## 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'
-- and map :: (a -> b) -> [a] -> [b] to be a special case
-- as well as having (.) :: (a -> b) -> (e -> a) -> (e -> b) as a
-- special case from the Functor instance for ((->) e)
-- Both notations can be provided to allow for clarity in different situations.
class Functor f where
map :: (a -> b) -> f a -> f b
(.) :: (a -> b) -> f a -> f b
map = (.)
(.) = map
-- should the Functor hierarchy proposal be adopted?
--
-- NO --
class Monad m where
(>>=) :: m a -> (a -> m b) -> m b
(>>) :: m a -> m b -> m b
return :: a -> m a
fail :: String -> m a
--
-- YES --
-- the following has been shamelessly copied
-- from the functor hierarchy proposal wiki page
class Functor f => Applicative f where
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?
-- my undestanding is that this is the default for monad
(>>) :: Applicative f => f a -> f b -> f b
fa >> fb = (map (const id) fa) <*> fb
-- this leaves little left for the actual Monad class
class (Applicative f) => Monad f where
(>>=) :: f a -> (a -> f b) -> f b
join :: f (f a) -> f a
x >>= f = join (map f x)
join x = x >>= id
-- end of Functor hierarchy dilemma
-- 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
class (MonadZero m) => MonadPlus m where
(++) :: m a -> m a -> m a
class (MonadZero m) => MonadOr m where
orElse :: m a -> m a -> m a
```

How to use it, as it stands,

```
import Prelude () -- hide everything
import TheOtherPrelude -- get everything
import qualified TheOtherPrelude.Monad.Kleisli as M -- standard convention
```

## See also

- Mathematical prelude discussion - A numeric Prelude. Could this be merged into this one?
- Prelude extensions and Prelude function suggestions - Unlike "The Other Prelude" they
*enhance*the Prelude. - Functor hierarchy proposal - making "Monad m" imply "Functor m"
- If-then-else - making "if" a function
- MissingH - functions "missing" from the haskell Prelude/libraries