[Rd] Trivial typo in help("browser")

[Rui Barradas]

Hello,

Double thanks, for the correction and for the lesson.
In particular, I had never noticed the f2() example's behavior.
It's always good to learn something new.

Rui Barradas


Às 08:57 de 29/07/21, Martin Maechler escreveu:
>>>>>> Rui Barradas
>>>>>>      on Thu, 29 Jul 2021 07:52:02 +0100 writes:
> 
>      > Hello,
> 
>      > R 4.1.0 on Ubuntu 20.04, session info below.
> 
>      > I am not an English native speaker but in help("browser"),
>      > section Arguments, argument expr, there is a wrong verb
>      > tense:
> 
>      > "invoked" should be "invoke", right?
> 
>      > expr An expression, which if it evaluates to TRUE the
>      > debugger will invoked, otherwise control is returned
>      > directly.
> 
>      > sessionInfo()   R version 4.1.0  .....
> 
> Thank you, Rui.   Indeed, there's a typo there.
> I claim that it is a missing 'be':  "be invoked" almost surealy
> was intended.
> 
> As we are on the R-devel mailing list, however, let's dig and learn a bit more:
> 
> Note that the *default*  is  `expr = TRUE`
> which is already a bit "special" for an "expression"..
> 
> Let's try to understand what was meant --- NB a strategy I
> strongly recommend even if you're somewhat experienced :
> 
>> ff <- function(x) { y <- x^2; browser("in ff():", expr = (y == 4)); y }
>> ff(1)
> [1] 1
>> ff(2)
> Called from: ff(2)
> Browse[1]> debug at #1: y
> Browse[2]> ls.str()
> x :  num 2
> y :  num 4
> Browse[2]> c
> [1] 4
>> ff(3)
> [1] 9
>>
> 
> So indeed, it does behave as I expected.
> A further experiment, play with
> 
>     f2 <- function(x, e=1) { y <- x^2; browser("in ff():", expr = e); y }
> 
> shows that  'evaluates to TRUE'  is also
> not as precise as it could be, and even "wrong":
>   'expr = pi'  also behaves as TRUE,  and even
>   'expr = NA'  behaves the same.
> 
> 
> I don't know when/how  `expr` was introduced (probably taken
> from 'S / S+' ..), but to me it seems actually somewhat a
> misnomer because in that generalized sense, *every*
> argument passed to an R function is an "expression".
> Instead, what counts is that a low-level as.logical(expr) is not TRUE.
> 
> So, yes, the documentation about `expr` definitely needs to be
> changed.
> 
> Unless I get convincing suggestions for improvements, I'll commit
> 
>    \item{expr}{a \dQuote{condition}.  By default, and whenever not false
>      after being coerced to \code{\link{logical}}, the debugger will be
>      invoked, otherwise control is returned directly.}
> 
> (and also amend the formulation a bit later on the help page
>   where expr is mentioned again).
> 
> Martin
> 
> 
>      > Thanks to all R Core Team members for their great work for
>      > all of us.
> 
>      > Hope this helps,
> 
>      > Rui Barradas
>