Introduces error variants for external crate errors and internal
errors.
Additional context can be provided at sites where errors occur using a
simple `.context()` call.
Implements the new backend trait for the FinitoPostgres type which
now represents instances of the Postgres backend.
This refactoring is not yet fully complete, as some restructuring of
the code is in order.
Changes the implementation of action execution to deal with the
returned associated errors.
The only sensible constraint on those errors that I could think of for
now is `Debug`, meaning that errors are now persisted as debug
messages.
This is not as nice to work with for a future implementation of
retryable actions as the equivalent in Haskell, but maybe an idea
shows up underway. The main issue is that most of the common error
types will not be implementing Serde traits, so serialization to/from
the same error type is difficult.
Adding an implementation constraint for JSON serialisation on error
types (i.e. `S::Error: Serialize + Deserialize`) would probably cause
headaches for users, especially if they are trying to use an
out-of-the-box error type or an error type wrapping foreign errors.
Det ska'kke være lett ...
Implements a simple model for executing actions which will run them in
sequence, synchronously, after advancing an FSM and committing the
initial transaction.
Note that multiple things are not yet taken into account:
* Error handling of actions (they can not currently fail)
* Retrying of actions
* Concurrency model
I started out by implementing the concurrency model similarly to the
green-threading method used in Hamingja (but using OS threads), but
slowly noticed that it may not be the best way to do that. It needs a
little bit of discussion.
Either way for most actions this method is fast enough to work for
implementing things on top of Finito's model.
Adds a test for the two most important functions in Finito's
PostgreSQL backend.
These actually require a local Postgres database to be available when
running. Currently the connection details are hardcoded in the test.
Adds the initial finito-postgres crate with type definitions for the
tables and initial functions to interact with persisted FSMs.
This is far from feature complete at this commit.
