Control.Comonad.Store.Class

class (Comonad w) <= ComonadStore s w | w -> s where

The ComonadStore type class represents those monads which support local position information via pos and peek.

• pos reads the current position.
• peek reads the value at the specified position in the specified context.

An implementation is provided for StoreT.

Laws:

• pos (extend _ x) = pos x
• peek (pos x) x = extract x

For example:

blur :: forall w. (ComonadStore Number w) -> w Number -> w Number
blur = extend \r -> (peeks (\n -> n - 1) r + peeks (\n -> n + 1) r) / 2)

Members

• pos :: forall a. w a -> s
• peek :: forall a. s -> w a -> a

Instances

• (Comonad w) => ComonadStore s (StoreT s w)
• (ComonadStore s w) => ComonadStore s (EnvT e w)
• (ComonadStore s w, Monoid m) => ComonadStore s (TracedT m w)

experiment :: forall s w a f. ComonadStore s w => Functor f => (s -> f s) -> w a -> f a

Extract a collection of values from positions which depend on the current position.

peeks :: forall w a s. ComonadStore s w => (s -> s) -> w a -> a

Extract a value from a position which depends on the current position.

seek :: forall w a s. ComonadStore s w => s -> w a -> w a

Reposition the focus at the specified position.

seeks :: forall w a s. ComonadStore s w => (s -> s) -> w a -> w a

Reposition the focus at the specified position, which depends on the current position.