Ideas.Common.Strategy.Choice

A type class for expressing choice, preference, and left-biased choice. The Menu datatype implements the type class by keeping all the alternatives.

Choice type class

class Choice a where

Laws: .|., ./. |> are all associative, and have empty as their unit element.

Minimal complete definition

empty, (.|.), (./.), (|>)

Methods

empty :: a

Nothing to choose from.

(.|.) :: a -> a -> a infixr 3

Normal (unbiased) choice.

(./.) :: a -> a -> a infixr 3

Left-preference.

(|>) :: a -> a -> a infixr 3

Left-biased choice.

choice :: [a] -> a

One of the alternatives in a list (unbiased).

preference :: [a] -> a

orelse :: [a] -> a

Instances

Choice [a]

Choice (Process a)

Choice (Strategy a)

Choice b => Choice (a -> b)

Choice (Menu k a)

Menu data type

data Menu k a

A menu offers choices and preferences. It stores singleton bindings (thus acting as a finite map) and one special element (doneMenu). It is an instance of the Functor and Monad type classes.

Instances

Functor (Menu k)

(Eq k, Eq a) => Eq (Menu k a)

Choice (Menu k a)

(|->) :: a -> s -> Menu a s infixr 5

Singleton binding

doneMenu :: Menu k a

Special element for denoting success

eqMenuBy :: (k -> k -> Bool) -> (a -> a -> Bool) -> Menu k a -> Menu k a -> Bool

Equality with a comparison function for the elements

Queries

elems :: Menu k a -> [(k, a)]

Returns all elements that are in the menu.

bests :: Menu k a -> [(k, a)]

Returns only the best elements that are in the menu with respect to left-biased choices.

bestsOrdered :: (k -> k -> Ordering) -> Menu k a -> [(k, a)]

Returns only the best elements that are in the menu, with a given ordering.

isEmpty :: Menu k a -> Bool

Is the menu empty?

hasDone :: Menu k a -> Bool

getByIndex :: Int -> Menu k a -> Maybe (k, a)

Get an element from the menu by its index.

cut :: Menu k a -> Menu k a

Only keep the best elements in the menu.

Generalized functions

onMenu :: Choice b => (k -> a -> b) -> b -> Menu k a -> b

Generalized monadic bind, with the arguments flipped.

onMenuWithIndex :: Choice b => (Int -> k -> a -> b) -> b -> Menu k a -> b

Maps a function over a menu that also takes the index of an element.