a version of source() which keeps comments ?
Thu, 20 Jun 2002 12:43:26 +0100 (BST)
On 20 Jun 2002, Peter Dalgaard BSA wrote:
> Martin Maechler <firstname.lastname@example.org> writes:
> > I'd like to have this to be used in, e.g.,
> > demo() and example().
> > Currently, source() parse()s the entire file and then evaluates
> > expression by expression. ``Of course'', parse() already loses
> > the comments.
> > An (much slower) alternative might be to the readLine() the
> > file, echo what we read,
> > and try to parse() ``the current chunk''.
> > when parse() fails (when the current expression is incomplete),
> > we silently read the next line, etc, until the expression is complete and hence
> > parse() succeeds, then we eval() and print().
> > What do people think?
> > Would there be volunteers to write this?
> > [I think it should finalize as an optional argument to source(),
> > but for experimentation it might be easier to try with a
> > function sourceLinewise(.)
> > ].
> Historically, this is what source() should have done all the time if
> it were to be in keeping with other Unix programs (shift input from
> stdin temporarily). The source() that we have is really "evaluate
> file". I don't think we can source() an infinite stream like a pipe or
> a socket, can we?
> Actually, I think it can be done with a little careful file descriptor
> switching. (Turn of readline processing, etc., switch stdin to file,
> run till eof or error, switch back and reestablish readline.) We'd
Rather, connection-switching. The Green book describes sink() as being
capable of switching the input connection, but it isn't like that
in any version of S-PLUS I have ever seen. I haven't thought through the
> still have the reparse-on-incomplete thing, since that also happens on
> stdin -- something I suspect isn't necessary, but it takes a fairly
> hard look at the grammar itself to find out.
> (This kind of stuff has long been on my might-do list of projects,
> along with (re)fixing the comment issue and providing better
> information on parse/eval errors. I'd better not feel possessive about
> the ideas...)
> O__ ---- Peter Dalgaard Blegdamsvej 3
> c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
> (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
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