Actions are essentially dynamic, computational entities.
The performance of an action directly represents information processing
behaviour and reflects the gradual, step-wise nature of computation. Items
of data are, in contrast, essentially static, mathematical
entities, representing pieces of information, e.g., particular numbers.
Of course actions are `mathematical' too, in the sense that they are abstract,
formally-defined entities, analogous to abstract machines defined in automata
theory. A yielder represents an unevaluated item of data,
whose value depends on the current information, i.e., the previously-computed
and input values that are available to the performance of the enclosing
action. For example, a yielder might always evaluate to the datum currently
stored in a particular cell, which could change during the performance of
an action. |