[Rd] identical(..., ignore.environment=TRUE)

[Duncan Murdoch]

On 11/10/2015 8:05 PM, Ben Bolker wrote:
> 
>   It seems odd/inconvenient to me that the "ignore.environment" argument
> of identical() only applies to closures (which I read as 'functions' --
> someone can enlighten me about the technical differences between
> functions and closures if they like -- see below for consequences of my
> confusion).  This is certainly not a bug, it's clearly documented, but
> it seems like a design flaw.  It would certainly be convenient to be
> able to ignore differences in environments when comparing complex
> objects with lots of deeply nested formula and terms objects with
> environments ...
> 
>    Can anyone suggest a reason for this design?
> 
> Example:
> 
>> f1 <- formula()
>> f2 <- formula()
>> environment(f2) <- new.env()
>> identical(f1,f2)
> [1] FALSE
>> identical(f1,f2,ignore.environment=TRUE)
> [1] FALSE
> 
> Actually, maybe I don't understand how this is supposed to work since I
> thought this would be TRUE:
> 
>> f1 <- function() {}
>> f2 <- function() {}
>> environment(f1) <- new.env()
>> environment(f2) <- new.env()
>> identical(f1,f2,ignore.environment=TRUE)   ## FALSE

Those two functions likely have different srcref attributes.  If you
created f2 using f2 <- f1, you'd get your expected result.

> 
>   Maybe the problem *is* that I don't know the difference between a
> function and a closure ... ?

In R, there is no difference.  All functions are closures.

Some people only use "closure" for functions returned as the value of
other functions.  That may be correct usage in other languages, but not
in R.

Duncan Murdoch