Gerry wrote:

Good!

As a data point, the approach that I have followed has been to
straightforwardly mimic the usual input stream words on a line
file input stream with a file text input buffer and parse area
and a file input stream stack.

So, there are words like:

LFSOURCE LFPARSE-AREA@ LFPARSE-AREA!
EMPTY-LFPARSE-AREA
LFPARSE LFPARSE-NAME
LFREFILL SAVE-LFIN RESTORE-LFIN

The user explicity opens and closes the file input stream, and
any of the usual parsing words, such as those in the ToolBelt,
can be mimicked pretty much by just inserting names like those
above in place of their counterparts.