[Rd] Bug in comparison of language objects?

[Duncan Murdoch]

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