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Directive Action Notation

Actions | Yielders | Data

Directive action notation is concerned with specifying the processing of a mixture of scoped and stable information, representing circular bindings by means of redirections.

Actions

indirectly bind T to Y | redirect T to Y | undirect T | recursively bind T to Y | indirectly produce Y

All primitive directive actions:
- Give no transients.
- Make no changes to storage.
- Do not communicate.
There are no special directive action combinators.
indirectly bind T to Y : a primitive directive action, where T is a token and Y is a yielder. Represents creating a piece of scoped information for subsequent redirection.
- Indivisible. Completes when Y yields data of sort bindable or the individual datum unknown . Fails otherwise.
- Produces the binding of the token T to an indirection.
- Augments the current redirections with the indirection, initialized to refer to the data yielded by Y .
redirect T to Y : a primitive directive action, where T is a token and Y is a yielder. Represents redirecting a piece of scoped information so as to create a circular structure.
- Indivisible. Completes when Y yields data of sort bindable or unknown . Fails otherwise.
- Produces no bindings.
- Redirects the indirection bound to T to refer to the data yielded by Y .
undirect T : a primitive directive action, where T is a token. Indicates that an indirection can be reused.
- Indivisible. Completes.
- Produces no bindings.
- Redirects the indirection bound to T to unknown , and makes it available for reuse.
recursively bind T to Y : a directive action, where T is a token and Y is a yielder. Represents creating a piece of scoped information and redirecting it so as to create a circular structure. The yielder Y is evaluated in the scope of an indirect binding for T .
- Indivisible. Completes when Y yields data of sort bindable (or unknown ). Fails otherwise.
- Produces the binding of the token T to an indirection.
- Augments the current redirections with the indirection, initialized to refer to the data yielded by evaluating Y using the current bindings overlaid by the indirect binding for T .
indirectly produce Y : a primitive directive action. Represents reflection of reified stable information.
- Indivisible. Completes when Y yields a datum of sort redirections.
- Makes the redirections yielded by Y .

Yielders

current redirections | indirect closure a

current redirections: a map yielder. Yields the state of the redirections.
indirect closure a: an abstraction yielder, where a is an abstraction. Yields an abstraction which incorporates the same action as a, except that the incorporated action has a snapshot of the current redirections, of use when the abstraction is to be enacted on another agent and the incorporated action depends on indirect bindings. (The indirections created on different agents are distinct, to avoid interference between the snapshot of redirections in an indirect closure and any redirections current on the agent where the closure is enacted.)
This operation extends to yielders Y in the usual way: it is evaluated by applying the above operation to the datum yielded by evaluating Y .

Data

redirections | indirection | indirect production d

redirections: a subsort of map . Its individuals represent collections of associations between indirections and bindable (or unknown ) individuals.
indirection: a subsort of distinct-datum . An indirection represents a point of circularity on a particular agent, but it can be re-produced on another agent (by a closure).
indirect production d : an abstraction, where d is redirections. Incorporates the action indirectly produce d . Useful when d is a redirections yielder. For example, an evaluation of indirect production current redirections yields an abstraction which, when enacted, always reflects the redirections received by the evaluation.

[Created by Jin Jin Yi and Ana Carla Santos. Last modified at 21 Dec 1997 by Ana Carla]