Attributes

A session carries named numeric attributes. Every name assigned by set or choose is an attribute of every session, starting at 0. The built-in ones below need no assignment. A name may not be both an attribute and a let constant, and neither may take a context variable's name.

Name	Set by	Meaning
serial	arrival	arrival order, counted from 0
turn_no	turn;	turns taken so far: 0 before the first turn;, 1 after it
cached	admission	units of the session's own cached prefix consumed at its last admission (reuse); 0 after the admission of a hold without cache, which consumes none
computed	preemption	the position the hold had computed when it was preempted; 0 on a first execution and after a hold completes

With a trace, turn; also sets:

Name	Meaning
new	new tokens this turn brings
out	output tokens of the turn
think	the think time the trace records for the turn
more	1 while another turn remains, 0 after the last
forced	1 if the trace forces the turn to miss the prefix cache (an optional sixth column, else 0)

cached and computed are set by the scheduler, so they cannot be hidden.

A program that resumes after a preemption reads computed; one that recomputes from the prompt alone does not read it.