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

[Tomas Kalibera]

For reference, this has been fixed so that the precedence of "?" is 
lower than "=", as documented.
Tomas

On 8/30/19 7:45 PM, peter dalgaard wrote:
> ...and 14955, which seems to have the explanation (but was marked as closed/fixed??). The parser does list '?' as lower precedence than '=', but '='-assignments are not normal 'expr's which can appear as arguments to '?'. (Presumably because of named arguments: f(a=b) differs from f(a<-b).)
>
> Other tokens which have lower precedence than assignments are flow-control items, IF ELSE WHILE FOR REPEAT, but I don't see any way to confuse them in the same way as '?'.
>
> It might be possible to resolve the situation by specifying '?' syntax explicitly as
> expr_or_assign '?' expr_or_assign, but, well, "There be Tygers here"...
>
> -pd
>
>
>> On 30 Aug 2019, at 18:32 , Kevin Ushey <kevinushey using gmail.com> wrote:
>>
>> 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
>>>>
>>>>
>>>>
>>>>
>>>> *******************************************************************
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