- Make Evaler mostly thread-safe. The only remaining thread-unsafe part is the
modules field, which is more tricky than other fields.
- Remove the state and evalerScopes type, and move their fields into Evaler.
- Expose valuePrefix via a get method, and change PortsFromFiles to take the
prefix instead of a *Evaler. Also expose a PortsFromStdFiles.
- Make Evaler a normal field of Frame, instead of an embedded field. This makes
access to global states more explicit.
Most of the places that need to directly call a function is in the edit package,
which need to call user-defined callbacks.
This change eliminates most call sites of NewTopFrame (including all call sites
outside the eval package). Remove the function and inline it in the remaining
few call sites.
Remove NewTopFrame means that the eval package no longer offers other packages
a way to construct Frame instances. This is intended: Frame is a relatively
low-level concept, and all code outside the eval package now uses the more
high-level Eval, Call, Check/CheckTree methods of *Evaler. The most notable
exception is packages that implement modules; they may still use Frame to access
the information kept in it, but they never construct Frame instances.
In future, the Frame type can be changed to an interface.
