R devel - Sep 2021 - Should Position() use match.fun()?

Hello,

All of the funprog functions except Position() use match.fun() early
in the body of the function. (Filter() seems to rely on lapply() for
this, but the effect is the same.) In most cases this isn't a problem,
but I can't see why Position() shouldn't look something like

Position2 <- function(f, x, right = FALSE, nomatch = NA_integer_) {
    f <- match.fun(f) # the only difference from Position()
    ind <- if (right) rev(seq_along(x)) else seq_along(x)
    for (i in ind) {
        if (f(x[[i]])) return(i)
    }
    nomatch
}

This would make it consistent with the other funprog functions, and
would mean that Find() and Position() give the same result when
expected
> equals3 <- function(x) x == 3
> Position("equals3", 1:5)
Error in f(x[[i]]) : could not find function
"f"
> Position2("equals3", 1:5)
[1] 3
> Find("equals3", 1:5)
[1] 3

Thanks,
Steve

>>>>> Steve Martin writes:
> Hello,
> All of the funprog functions except Position() use match.fun() early
> in the body of the function. (Filter() seems to rely on lapply() for
> this, but the effect is the same.) 
Right. 
> In most cases this isn't a problem, but I can't see why Position()
> shouldn't look something like
> Position2 <- function(f, x, right = FALSE, nomatch = NA_integer_) {
>     f <- match.fun(f) # the only difference from Position()
>     ind <- if (right) rev(seq_along(x)) else seq_along(x)
>     for (i in ind) {
>         if (f(x[[i]])) return(i)
>     }
>     nomatch
> }
> This would make it consistent with the other funprog functions, and
> would mean that Find() and Position() give the same result when
> expected
Indeed.  I'll look into adding the match.fun ...

Best
-k
>> equals3 <- function(x) x == 3
>> Position("equals3", 1:5)
> Error in f(x[[i]]) : could not find function "f"
>> Position2("equals3", 1:5)
> [1] 3
>> Find("equals3", 1:5)
> [1] 3
> Thanks,
> Steve
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