[Rd] Mapping parse tree elements to tokens

[Duncan Murdoch]

On 29/07/2015 2:30 PM, Michael Lawrence wrote:
> Probably need a generic tree based on "ParseNode" objects that
> associate the line information with the symbol (for leaf nodes). As
> Duncan notes, it should be possible to gather that from the table.
>
> But it would be nice if there was an "expr" column in the parse data
> column in addition to "text". It would contain the parsed object.
> Otherwise, to use the table, one is often reparsing the text, which
> just seems redundant and inconvenient.

Can you (both Jim and Michael) describe the uses you might have for 
this?  There are lots of possible changes that could make this 
information available:

  - attach to each item in the parse tree, as the parser package did.  
(Bad idea for general use which is why I dropped it, but
it could be done as a special option to parse, if you aren't planning to 
evaluate the expression.)
  - give the index into the parse tree of each item, i.e. c(1,1), 
c(1,2), c(1,3) in the example below, or just 1,2,3 along with a function 
to reconstruct the full path.
  - give a copy of the branch of the parse tree, as Michael suggests.

etc.  Which is best for your purposes?

Duncan Murdoch

>
> Michael
>
> On Wed, Jul 29, 2015 at 9:43 AM, Duncan Murdoch
> <murdoch.duncan at gmail.com> wrote:
> > On 29/07/2015 12:13 PM, Jim Hester wrote:
> >>
> >> I would like to map the parsed tokens obtained from utils::getParseData()
> >> to the parse tree and elements obtained by base::parse().
> >>
> >> It looks like back when this code was in the parser package the parse()
> >> function annotated the elements in the tree with their id, which would
> >> allow you to perform this mapping.  However when the code was included in
> >> R
> >> this functionality was removed.
> >
> >
> > Yes, not all elements of the parse tree can legally have attributes
> > attached.
> >>
> >>
> >> ?getParseData states
> >>    The ‘id’ values are not attached to the elements of the parse
> >>            tree, they are only retained in the table returned by
> >>            ‘getParseData’.
> >>
> >> Is there another way you can map between the getParseData() tokens and
> >> elements of the parse tree that makes this additional annotation
> >> unnecessary?  Or is this simply not possible?
> >
> >
> > I think you can't get to it, though you can get close by looking at the id &
> > parent values in the table.  For example,
> >
> >  code <- "x + (y + 1)"
> >  p <- parse(text=code)
> >
> > getParseData(p)
> >    line1 col1 line2 col2 id parent     token terminal text
> > 15     1    1     1   11 15      0      expr    FALSE
> > 1      1    1     1    1  1      3    SYMBOL     TRUE    x
> > 3      1    1     1    1  3     15      expr    FALSE
> > 2      1    3     1    3  2     15       '+'     TRUE    +
> > 13     1    5     1   11 13     15      expr    FALSE
> > 4      1    5     1    5  4     13       '('     TRUE    (
> > 11     1    6     1   10 11     13      expr    FALSE
> > 5      1    6     1    6  5      7    SYMBOL     TRUE    y
> > 7      1    6     1    6  7     11      expr    FALSE
> > 6      1    8     1    8  6     11       '+'     TRUE    +
> > 8      1   10     1   10  8      9 NUM_CONST     TRUE    1
> > 9      1   10     1   10  9     11      expr    FALSE
> > 10     1   11     1   11 10     13       ')'     TRUE    )
> >
> >
> > Now p is an expression, with the parse tree in p[[1]].  From the table, we
> > can see that the root node has id 15, and 3 nodes have that as a parent.
> > Those would be p[[c(1,1)]], p[[c(1,2)]], p[[c(1,3)]].  The tricky part is
> > the re-ordering:  those correspond to `+`, x, and (y+1) respectively, not
> > the order they appear in the original source or in the table.  Generally the
> > function call appears first in the parse tree, but I'm not sure you could
> > always recognize which is the function call by looking at the table.
> >
> > Duncan Murdoch
> >
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