[R] evaluating expressions as R console

[Adrian Dușa]

I think I have found a working solution. Rather ugly, but working and will
keep looking for better alternatives, though.

The procedure involves:

- parsing one line at a time
- if incomplete, parse as many lines as necessary to form an expression
- determine all expressions in the original input
- evaluate each expression, one at a time
  (which shows individual errors and warnings)
- print each pair of:
    - expression
    - error, or result with possible warning(s)

It works reasonably quick for small chunks, but that is ok for my purposes.

I hope it helps anyone. Should there be better alternatives, I would be
more than grateful for a hint.

Best,
Adrian

On Mon, Sep 5, 2016 at 5:33 PM, Bert Gunter <bgunter.4567 at gmail.com> wrote:

> I'm sharing this with r-help, as your detailed response might help
> others help you.
>
> -- Bert
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>
>
> On Sun, Sep 4, 2016 at 11:45 PM, Adrian Dușa <dusa.adrian at unibuc.ro>
> wrote:
> > On Mon, Sep 5, 2016 at 2:52 AM, Bert Gunter <bgunter.4567 at gmail.com>
> wrote:
> >>
> >> You might want to look at the "evaluate" package.
> >
> >
> > Of course, forgot to mention. I did try it, but got:
> >
> >> bar <- readLines("foo.R", warn = FALSE)
> >> bar <- paste(bar, collapse = "\n")
> >> evaluate::evaluate(input = bar)
> > [[1]]
> > $src
> > [1] "foo <- function(x) {\n    print(x)\n}\nprint)foo)\nfoo(2)"
> >
> > attr(,"class")
> > [1] "source"
> >
> > [[2]]
> > <simpleError: <text>:4:6: unexpected ')'
> > 3: }
> > 4: print)
> >         ^>
> >
> > I ran into the same problem as source(): it works only if it doesn't have
> > any errors. In addition, the error message is also different because it
> > evaluates the entire chunk, whereas the R console evaluates one command
> > (line) at a time.
> >
> > Fixing the command:
> > bar2 <- "foo <- function(x) {\n    print(x)\n}\nprint(foo)\nfoo(2)"
> >
> > will fix the workflow in evaluate():
> >
> > evaluate::evaluate(input = bar2)
> >
> >
> > But it will also fix it with source():
> >
> >> source("foo2.R", echo = TRUE, keep.source = TRUE)
> >
> >> foo <- function(x) {
> > +     print(x)
> > + }
> >
> >> print(foo)
> > function(x) {
> >     print(x)
> > }
> >
> >> foo(2)
> > [1] 2
> >
> >
> > So evaluate() has more detail than source(), but essentially they do the
> > same thing in evaluating the whole chunk. From the help of source():
> > "Since the complete file is parsed before any of it is run, syntax errors
> > result in none of the code being run."
> >
> > So far, it seems that only R CMD BATCH is able to run one command at a
> time:
> >
> > $ R CMD BATCH -q foo.R
> > $ cat foo.Rout
> >> foo <- function(x) {
> > +     print(x)
> > + }
> >> print)foo)
> > Error: unexpected ')' in "print)"
> > Execution halted
> >
> > This error is exactly the same as in the R console, and the function
> foo()
> > is created before the error occurs. One possible solution is to get the
> > workspace saved, and run R CMD BATCH again on the rest of commands after
> the
> > error.
> >
> > But it still needs additional objects if the chunk is to be evaluated in
> a
> > specific environment. This is the point where I've got, and I don't know
> if
> > this is the best approach.
> >
> > Thank you,
> > Adrian
>


-- 
Adrian Dusa
University of Bucharest
Romanian Social Data Archive
Soseaua Panduri nr.90
050663 Bucharest sector 5
Romania

	[[alternative HTML version deleted]]