A script whose first lines name an engine with `#targetengine name` (or
`//@targetengine name`) runs in that engine, and a later script that names
it sees the globals and functions earlier runs left, until the engine is
dropped or the session ends. A script without the line, and
`#targetengine main`, still get a new engine for each run.
- A session keeps at most 8 named engines, each with a 64 MiB heap. A run
that goes past the heap ends with the heap limit, and the engine stays
usable. Names are 1 to 64 bytes. The line comes once, in the script
itself, before its code and its #include lines.
- An uncaught error, a limit or script.stop puts the documents back and
keeps the globals the run set. An internal error drops the engine. A run
stopped at a dialog or left paused ends where it was before the engine
is kept. An error in a function an earlier run defined is reported
without a line and column.
- `vc`, `$`, `alert`, `confirm` and `prompt` are made once for each engine
and act for the run that calls them, including copies an earlier run kept
in a global. `vc.args` gives a read-only copy of the calling run's
`args`, and what a run sets on `$` lasts for that run only.
- `script.engines` lists the named engines with their heap, and
`script.engine.drop {name}` drops one. Scripts cannot run either.
- The engines stay on the thread that made them. A session used on
another thread starts there with no named engines, and the old ones are
dropped on their own thread.
- The web build has no named engines: a run that names one other than
`main` ends with an error before any of it runs.
- `Realm::end` ends a run where it is, `Realm::error_source` counts from
the realm's last script, and `HostItem::FrozenGetter` gives a frozen
value each time it is read.
- The script checker lists `#targetengine` as a supported directive.
Docs: docs/mcp.md, docs/target-app-parity.md, docs/gaps.md.
alert(message[, title, errorIcon]), confirm(message[, noAsDflt, title])
and prompt(message, preset[, title]) are globals in a script run. In the
app the run waits at the call for the person's answer, spends no
instructions while it waits, and every dialog has Stop, which ends the
run and puts every document back. A run over MCP or the command line
takes its answers in order from script.run's answers, a list of
{kind, value} records; a missing, mismatched or unused answer ends the
run. The report lists each dialog with its answer in dialogs, with
dialogCount and dialogsTruncated.
The interpreter gains a host call that waits at the call for its
result, from the script's own code only; a dialog called in a callback
of a built-in, a getter or a conversion throws in the app.
Docs: docs/mcp.md, docs/target-app-parity.md.
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