Function closure constructions

I think that passing around functions as data is a under-loved capability of R and I think part of it is how cumbersome it is to build a closure of a partially evaluated function, instead any functions-as-data approach requires building functions that return functions, encapsulating a few arguments.

Instead, it would be amazing if we could say "I'm not done specifying arguments yet"

```r
sum_one_plus <- sum(1).. # this says "I'm not done" and produces a partially evaluated function
sum_one_plus(2, 3, 4)
# [1] 10
```

_alternatively_

```r
sum_one_plus <- sum(1, ..) # perhaps too similar to ellipsis, although those might need to be named
sum_one_plus(2, 3, 4)
# [1] 10
```

Under the hood, this produces a new function call which starts to populate the function's internal environment with matched arguments and trims those matched arguments from the remaining function signature.