A recent change to Racket must have changed the way `for` expands,
because now in conjunction with `local-expand`, we see *effectively* a
`(begin (values) (void))`. This isn't a problem usually, but in
`#lang syndicate`'s `module-begin` context, we split apart `begin`s
and examine their constituents, leading to examination of something
that will ultimately yield 0 values.
The change accepts either 0 or 1 values when collecting actions for
the module's main boot actor to execute. More than 1 value yielded by
such an expression is still considered an error. Currently, it gives
unhelpful error location information; a future refinement might be to
make the error reporting for this (rare) situation more helpful.
This means that `*gc-priority*` scripts will now reliably run last.
Prior to this change, if some higher-priority script X ran while a
`*gc-priority*` script Y was queued, and it enqueued a high-priority
script Z, then Y would run before Z.
This is a major change to the previous design, and also a change with
respect to the semantics in the ESOP 2016 paper. All the complexity of
echo-cancellation is stripped out of the core dataspace semantics, and
the relaying protocol is changed from one constructor, `at-meta`, to
two, `inbound` and `outbound`. The relay connecting a dataspace to its
container is now completely symmetric with the contained actors: it
initially asserts interest in what it is to relay, just like any other
actor would. Dataspaces no longer treat relaying specially.
This commit has updated all (I think) of the non-graphical examples. The
graphical code remains to be done in a following commit.
A store is like a parameter, except stores are independent of each
other, unlike parameters which are bundled together into a single
parameterization. This was observable in cases like the
example-action-after-suspension code checked in here, where dataflow
invoked a script, which parameterized current-dataflow-subject-id.
This captured *too much* of things like the pending-patch and
pending-actions. Subsequent `schedule-action!` calls' effects were
then lost.
Introduced expanders for events (define-event-expander) and for
assertion-patterns (define-assertion-expander).
Introduced convenience syntax and utilities in web.rkt for working
with web requests.
Support nested bindings in assertion-patterns for message events
(only).
Tony Garnock-Jones
Sam Caldwell