Atomic tuple update

[lou1306]

Suppose <var1, var2> is a tuple inside some stigmergy.

Right now an agent can only update the variables one at a time:

var1 <~ expr1; var2 <~ expr2; ...

In some scenarios, however, it would be useful to allow for an atomic update of both values. Proposed syntax is

var1, var2 <~ expr1, expr2

which should avoid conflicts with the existing constructs

[lou1306]

Let us generalize this:

• let r = r1, ..., rn be a sequence of (distinct) references to interface (r. stigmergic, environment) variables
• let e1, ..., en a sequence of expressions

Then the basic process r1, ... rn <- e1, ..., en (r. r1, ... rn <~ e1, ..., en, r1, ... rn <-- e1, ..., en ):

1. evaluates e1, ..., en against the current state of the agent. Let v1, ..., vn the resulting values
2. assigns each v_i to the corresponding r_i.

Notice that after the process is completed, the global clock will have been increased n times. Currently, this has no consequences, as tupled stigmergic variables still end up with equal timestamps. However, we should correct this if we want use the global clock for other things in the future.