[Rd] ?Syntax wrong about `?`'s precedence ?

[Kevin Ushey]

See also: https://bugs.r-project.org/bugzilla/show_bug.cgi?id=16710

On Fri, Aug 30, 2019 at 9:02 AM William Dunlap via R-devel
<r-devel using r-project.org> wrote:
>
> Precedence is a property of the parser and has nothing to do with the
> semantics assigned to various symbols.  Using just core R functions you can
> see the precedence of '?' is between those of '=' and '<-'.
>
> > # '=' has lower precedence than '?'
> > str(as.list(parse(text="a ? b = c")[[1]]))
> List of 3
>  $ : symbol =
>  $ : language `?`(a, b)
>  $ : symbol c
> > str(as.list(parse(text="a = b ? c")[[1]]))
> List of 3
>  $ : symbol =
>  $ : symbol a
>  $ : language `?`(b, c)
> > # '<-' has higher precedence than '?'
> > str(as.list(parse(text="a ? b <- c")[[1]]))
> List of 3
>  $ : symbol ?
>  $ : symbol a
>  $ : language b <- c
> > str(as.list(parse(text="a <- b ? c")[[1]]))
> List of 3
>  $ : symbol ?
>  $ : language a <- b
>  $ : symbol c
>
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
>
> On Fri, Aug 30, 2019 at 4:41 AM Stephen Ellison <S.Ellison using lgcgroup.com>
> wrote:
>
> > > From: R-devel [mailto:r-devel-bounces using r-project.org] On Behalf Of Ant F
> > > Sent: 29 August 2019 12:06
> > > To: r-devel using r-project.org
> > > Subject: [Rd] ?Syntax wrong about `?`'s precedence ?
> > > ...
> > > See the following example :
> > >
> > >     `?` <- `+`
> >
> > I'm curious; What did you expect to happen if you replace the function '?'
> > with the operator '+' ?
> > ? is surely now being evaluated as a user-defined function and not as an
> > operator.
> > Would you expect the results of doing that to be the same as evaluation
> > without replacement?
> >
> > S Ellison
> >
> >
> >
> >
> > *******************************************************************
> > This email and any attachments are confidential. Any u...{{dropped:10}}
>
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