Also replace (*Frame).OutputChan with (*Frame).ValueOutput, which returns a
small interface for writing to the value output that is also aware when the
reader is gone.
- 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.
- Remove the Op type; it is no longer used by any code outside the eval package
and its use within the package is limited.
- Replace (*Evaler).execOp with (*Evaler).prepareFrame.
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.
This feature supersedes the CompileWithGlobal method, and simplifies the only
use of that method in pkg/edit, where the default binding is evaluated using the
edit: namespace as the global Ns.
Introduces two functions, PipePort and CapturePort, and implement output capture
in terms of them. These two functions return *Port instances, which can also be
used in (*Evaler).Eval calls.
