Enabled: An object is invoked with one of several selectors, each associated
with a sequence of arguments.
Functions or procedures (from math and
early computer languages) are invoked with no selector and a single
sequence of arguments. For objects to act like functions, we need a
convention for a default selector name that means "no interesting
selector here". Smalltalk uses "value" and "value:". Joule uses
"::". Java has no general convention, but java.lang.Runnable is
essentially a no-argument, void-return procedure, using the selector
"run", so in our interest in being standard, we respect this
precedent.
