Data.Propagator.Cell

This module exports the types and functions needed to create cells, manipulate their data and wire them up for data propagation.

Cell Creation and Inspection

data Cell s a

The type of a cell holding a value of type a. The type parameter s serves to keep the internal states of different cell networks separate from each other (see ST for details).

Instances

Eq (Cell s a)

Defined in Data.Propagator.Cell

Methods

(==) :: Cell s a -> Cell s a -> Bool

(/=) :: Cell s a -> Cell s a -> Bool

cell

Arguments

:: a

The initial value of the cell.

-> (a -> a -> Change a)

A function that describes how to join an existing cell value with a new one that the cell has received via propagation.

-> ST s (Cell s a)

The newly constructed cell.

Constructs a new cell with a given initial value and a function which defines how to react if a new value is about to be written to the cell.

readCell :: Cell s a -> ST s a

Reads the value of a specific cell.

writeCell :: a -> Cell s a -> ST s (Propagation s)

Writes a new value to a specific cell and starts to propagate potential changes through the network of connected cells.

Cell Connection

connect

Arguments

:: Cell s a

The source cell.

-> Cell s b

The target cell.

-> (a -> ST s b)

A function that describes how the value for the target cell is constructed, based on the value of the source cell.

-> ST s ()

Note that no propagation takes place (i.e., no Propagation is returned).

Connects a source cell to a target cell in order to propagate changes from the source to the target.

Note that newly connected cells do not start to propagate changes immediately after wiring up. Use propagate or propagateMany to do this.

sync :: Cell s a -> Cell s a -> ST s ()

Connects and synchronizes two cells, i.e. new values are propagated from the source to the target cell, and vice versa. Short form of syncWith id id.

Note that newly connected cells do not start to propagate changes immediately after wiring up. Use propagate or propagateMany to do this.

syncWith :: (a -> b) -> (b -> a) -> Cell s a -> Cell s b -> ST s ()

Connects and synchronizes two cells using two translation functions f and g, i.e. new values are propagated from the source to the target cell using f, and vice versa using g.

Note that newly connected cells do not start to propagate changes immediately after wiring up. Use propagate or propagateMany to do this.

Value Propagation

data Propagation s

The result of a propagation which allows to rollback changes and inspect its success.

undo :: Propagation s -> ST s ()

An action that reverts all cell changes of a propagation (both direct and transitive ones).

succeeded :: Propagation s -> Bool

True if the propagation was successful (i.e., it did not lead to a cell change that is Incompatible), otherwise False.

Note that unsuccessful propagations are not automatically reverted. Use undo to do this.

propagate :: Cell s a -> ST s (Propagation s)

Propagates the value of a specific cell to its connected cells in a transitive manner. The propagation ends if no more cell changes occur or if an Incompatible cell value change is encountered.

propagateMany :: [Cell s a] -> ST s (Propagation s)

Propagates the values of specific cells to their connected cells in a transitive manner. The propagation ends if no more cell changes occur or if an Incompatible cell value change is encountered.

label

Arguments

:: (a -> [b])

A function which extracts testable values from a cell content.

-> (b -> a)

A function which translates a testable value into a value which can be written back to the cell.

-> [Cell s a]

The set of cells for which the values are enumerated.

-> ST s [[b]]

Returns all valid assignments for the given cells.

If the content of a Cell s a is an accumulation of multiple values [b], and every value b itself can be used as content a for the cell, then we can write every value b one after another to the cell and check if the network converges to a successful state.

As a result, we can enumerate all possible combinations of valid values for a given set of cells. This is often used in constraint solving algorithms.