[Rd] withAutoprint({ .... }) ?

[Martin Maechler]

>>>>> William Dunlap <wdunlap at tibco.com>
>>>>>     on Fri, 2 Sep 2016 08:33:47 -0700 writes:

    > Re withAutoprint(), Splus's source() function could take a expression
    > (literal or not) in place of a file name or text so it could support
    > withAutoprint-like functionality in its GUI.  E.g.,

    >> source(auto.print=TRUE, exprs.literal= { x <- 3:7 ; sum(x) ; y <- log(x)
    > ; x - 100}, prompt="--> ")
    --> x <- 3:7
    --> sum(x)
    > [1] 25
    --> y <- log(x)
    --> x - 100
    > [1] -97 -96 -95 -94 -93

    > or

    >> expr <- quote({ x <- 3:7 ; sum(x) ; y <- log(x) ; x - 100})
    >> source(auto.print=TRUE, exprs = expr, prompt="--> ")
    --> x <- 3:7
    --> sum(x)
    > [1] 25
    --> y <- log(x)
    --> x - 100
    > [1] -97 -96 -95 -94 -93

    > It was easy to implement, since exprs's default value is parse(file) or
    > parse(text=text), which source is calculating anyway.


    > Bill Dunlap
    > TIBCO Software
    > wdunlap tibco.com

Thank you, Bill  (and the other correspondents); that's indeed a
very good suggestion :

I've come to the conclusion that Duncan and Bill are right:  One
should do this in R (not C) and as Bill hinted, one should use
source().  I first tried to do it separately, just "like source()",
but a considerable part of the source of source()  {:-)} is
about using src attributes instead of deparse() when the former
are present,  and it does make sense to generalize
withAutoprint() to have the same feature, so after all, have it
call source().

I've spent a few hours now trying things and variants, also
found I needed to enhance source()  very slightly also in a few
other details, and now (in my uncommitted version of R-devel), 

  withAutoprint({ x <- 1:12; x-1; (y <- (x-5)^2); z <- y; z - 10 })

produces

> withAutoprint({ x <- 1:12; x-1; (y <- (x-5)^2); z <- y; z - 10 })
> x <- 1:12
> x - 1
 [1]  0  1  2  3  4  5  6  7  8  9 10 11
> (y <- (x - 5)^2)
 [1] 16  9  4  1  0  1  4  9 16 25 36 49
> z <- y
> z - 10
 [1]   6  -1  -6  -9 -10  -9  -6  -1   6  15  26  39
> 

and is equivalent to 

   withAutoprint(expression(x <- 1:12, x-1, (y <- (x-5)^2), z <- y, z - 10 ))

I don't see any way around the "mis-feature" that all "input"
expressions are in the end shown twice in the "output" (the
first time by showing the withAutoprint(...) call itself).

The function *name* is "not bad" but also a bit longish;
maybe there are better ideas?  (not longer, no "_" - I know this
      	    	       	        is a matter of taste only)

Martin

    > On Fri, Sep 2, 2016 at 4:56 AM, Martin Maechler <maechler at stat.math.ethz.ch>
    > wrote:

    >> On R-help, with subject
    >> '[R] source() does not include added code'
    >> 
    >> >>>>> Joshua Ulrich <josh.m.ulrich at gmail.com>
    >> >>>>>     on Wed, 31 Aug 2016 10:35:01 -0500 writes:
    >> 
    >> > I have quantstrat installed and it works fine for me.  If you're
    >> > asking why the output of t(tradeStats('macross')) isn't being
    >> printed,
    >> > that's because of what's described in the first paragraph in the
    >> > *Details* section of help("source"):
    >> 
    >> > Note that running code via ‘source’ differs in a few respects from
    >> > entering it at the R command line.  Since expressions are not
    >> > executed at the top level, auto-printing is not done.  So you will
    >> > need to include explicit ‘print’ calls for things you want to be
    >> > printed (and remember that this includes plotting by ‘lattice’,
    >> > FAQ Q7.22).
    >> 
    >> 
    >> 
    >> > So you need:
    >> 
    >> > print(t(tradeStats('macross')))
    >> 
    >> > if you want the output printed to the console.
    >> 
    >> indeed, and "of course"" ;-)
    >> 
    >> As my subject indicates, this is another case, where it would be
    >> very convenient to have a function
    >> 
    >> withAutoprint()
    >> 
    >> so the OP could have (hopefully) have used
    >> withAutoprint(source(..))
    >> though that would have been equivalent to the already nicely existing
    >> 
    >> source(.., print.eval = TRUE)
    >> 
    >> which works via the  withVisible(.) utility that returns for each
    >> 'expression' if it would auto print or not, and then does print (or
    >> not) accordingly.
    >> 
    >> My own use cases for such a withAutoprint({...})
    >> are demos and examples, sometimes even package tests which I want to print:
    >> 
    >> Assume I have a nice demo / example on a help page/ ...
    >> 
    >> foo(..)
    >> (z <- bar(..))
    >> summary(z)
    >> ....
    >> 
    >> where I carefully do print parts (and don't others),
    >> and suddenly I find I want to run that part of the demo /
    >> example / test only in some circumstances, e.g., only when
    >> interactive, but not in BATCH, or only if it is me, the package maintainer,
    >> 
    >> if( identical(Sys.getenv("USER"), "maechler") ) {
    >> foo(..)
    >> (z <- bar(..))
    >> summary(z)
    >> ....
    >> }
    >> 
    >> Now all the auto-printing is gone, and
    >> 
    >> 1) I have to find out which of these function calls do autoprint and wrap
    >> a print(..) around these, and
    >> 
    >> 2) the result is quite ugly (for an example on a help page etc.)
    >> 
    >> What I would like in a future R, is to be able to simply wrap the "{
    >> .. } above with an 'withAutoprint(.) :
    >> 
    >> if( identical(Sys.getenv("USER"), "maechler") ) withAutoprint({
    >> foo(..)
    >> (z <- bar(..))
    >> summary(z)
    >> ....
    >> })
    >> 
    >> Conceptually such a function could be written similar to source() with an R
    >> level for loop, treating each expression separately, calling eval(.) etc.
    >> That may cost too much performnace, ... still to have it would be better
    >> than
    >> not having the possibility.
    >> 
    >> ----
    >> 
    >> If you read so far, you'd probably agree that such a function
    >> could be a nice asset in R,
    >> notably if it was possible to do this on the fast C level of R's main
    >> REPL.
    >> 
    >> Have any of you looked into how this could be provided in R ?
    >> If you know the source a little, you will remember that there's
    >> the global variable  R_Visible  which is crucial here.
    >> The problem with that is that it *is* global, and only available
    >> as that; that the auto-printing "concept" is so linked to "toplevel
    >> context"
    >> and that is not easy, and AFAIK not so much centralized in one place in the
    >> source. Consequently, all kind of (very) low level functions manipulate
    >> R_Visible
    >> temporarily.... and so a C level implementation of  withAutoprint() may
    >> need considerable more changes than just setting R_Visible to TRUE in one
    >> place.
    >> 
    >> Have any efforts / experiments already happened towards providing such
    >> functionality ?
    >> 
    >> ______________________________________________
    >> R-devel at r-project.org mailing list
    >> https://stat.ethz.ch/mailman/listinfo/r-devel

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