Operation to load an implicit, dynamic state value.

Operation to save an implicit, dynamic state value.

Computations which may load or save an implicit, dynamic state value.

An endofunctor corresponding to Stateful effect handlers.

Handles Stateful computations. Usage:

>>> let (nine, three) = state_handler 3 (load >>= \n -> save (n * n) >> return n)
>>> nine
9
>>> three
3

A "forwarding" state-handler.

A state-handler which forwards unsupported operations to another handler. Usage:

>>> (nine, unit) <- f_state_handler 3 (load >>= \n -> save (n * n))
>>> nine
9
>>> unit
()

Operation to throw a specified value in Exceptional circumstances.

A computation which evaluates to a Except for errors.

This handler Results in Either an err value or answer a.

Evaluates an exception-handling computation.

A more conventional throw-receiving idiom.

With a little elbow grease this could be derived automatically.

Example computation combining Stateful and Except effects, which were defined in a separate module. The parlor trick here is that this type-checks without defining any handlers, combining 3 operations from 2 distinct effect types with existing, independent handlers.

Interprets StatefulExcept err s a as the type s -> (s, Either err a).

A handler for both Stateful and Exceptional computations. If the typeclass instances above are the case-statements for different effects, this is more or less the case-statement for "return" / termination.

>>> effects_demo
(0,Right ())
(0,Left "error")

A Cell is either "on" (I) or "off" (O).

A background pattern to evaluate in our CA

Lifts a list of Cells into a Tape.

The 2-dimensional cellular automaton "rule 110." To evaluate one time-step, each cell along with its immediate left and right neighbors is used to determine that cell's next value (proceed below). I believe it is the simplest Turing-complete CA.

A 2-dimensional sheet (Sheet2). Each Cell of the Sheet2 is a function which transforms a Sheet2 of Cells into a new value for that Cell.

This lifts a pattern of Cell values into a 2-dimensional spreadsheet.

Prints a given slice of the output stream, which represents the evolution of the 2-D spreadsheet over time.

Constructs an interesting-ish Rule 110 scenario and prints a slice of the output stream, showing the time-evolution of a 2-D spreadsheet. This aims son_a and son_b at each other. They collide, entangle, and then disentangle in swapped places.

Some Cell patterns which happen to be interesting in Rule 110.

Some Cell patterns which happen to be interesting in Rule 110.

Some Cell patterns which happen to be interesting in Rule 110.