If you change `racket-bitsyntax` to use `typed/racket/base/no-check`
for its `bitstring.rkt` module, this runs about 15x faster than the
`syndicate` version of the stack. Otherwise, it runs about 3x faster
than the `syndicate` version of the stack.
Instead of having restriction-paths as an adjunct to a change, they're
more propertly a part of each assertion itself. The new `skeleton.rkt`
keeps an optional restriction-path with each assertion, treating it as
distinct from its underlying assertion. The idea of not signalling
changes in assertions that have a restriction-path mismatch stays.
This is used when relaying: because we don't have access to the full
term, but only the projection results, we are inserting various
`(discard)`s. This is the cause of the failure in
`test/core/nesting-confusion.rkt`.
By adding `restriction-path`, we allow the inner dataspace to avoid
showing a reconstructed term to endpoints that might be able to
observe the reconstructed parts.
An alternative implementation approach is to generalize patterns in
the inner relay actor, translating all `(discard)`s into captures,
which would give us all the relevant terms that we need. The way I've
chosen to go (or at least, to try out) allows us to potentially keep
the "efficient" idea of just transmitting pattern-bound values across
some network link connecting dataspaces. The alternative would require
transmission of the full assertions, eliding no irrelevant detail.
It's also nicely fast compared to the old-Syndicate version :-)
There are still some problems with parameters in cross-ds relaying;
the symptom is #f for (current-facet) at some point, leading to some
sprites that don't get retracted (!).
Tony Garnock-Jones