[Rd] Bug in comparison of language objects?

[Martin Maechler]

>>>>> Duncan Murdoch 
>>>>>     on Tue, 20 Feb 2024 08:47:30 -0500 writes:

    > On 20/02/2024 8:03 a.m., Duncan Murdoch wrote:
    >> I noticed the following odd behaviour today:
    >> 
    >> exprs <- expression( mean(a), mean(b), { a }, { b } )
    >> 
    >> exprs[[1]] == exprs[[2]] #> [1] FALSE
    >> 
    >> exprs[[3]] == exprs[[4]] #> [1] TRUE
    >> 
    >> Does it make sense to anyone that the argument passed to
    >> `mean` matters, but the expression contained in braces
    >> doesn't?

    > I have done some debugging, and found the cause: for the
    > comparison of language objects, R deparses them to strings
    > using C function deparse1(), and looks at only the first
    > line.  "mean(a)" deparses as is, but "{ a }" deparses to 3
    > lines

    > { a }

    > and the first line is the same as for "{ b }", so they
    > compare equal.

    > I think it would make more sense to deparse them to one
    > long string, and compare those, i.e. to replace deparse1()
    > with deparse1line() (which may have been the intention).

    > Duncan Murdoch

I agree ... (and more do).
Thank you for  adding it as formal report to R's bugzilla,
https://bugs.r-project.org/show_bug.cgi?id=18676

Unfortunately, it triggers something in the (byte) compiler test
suite, and (also/hence) will probably be too late for R 4.3.3.

Martin

Martin Maechler