[R] chaining closure arguments on-the-fly

[Duncan Murdoch]

On 20/06/2020 7:15 a.m., Benjamin Tyner wrote:
> Greetings,
> 
> Occasionally, I desire to call a function with one argument set to equal
> to another. Here is a toy example:
> 
>      f <- function(x, y) {
> 
>          x + y
>      }
> 
>      f(x = 3, y = x) # Error in f(x = 3, y = x) : object 'x' not found
> 
> So far, the most concise way I found to accomplish this is:
> 
>      f(x = 3, y = local(sys.frame(1)$x)) # evaluates to 6
> 
> but I dislike this solution because local() creates a new environment.
> Surely there must be a better way?
> 
> Note: I'm not interested in solutions that require modifying or currying f.

How about

g <- function(x, y = x) {
   f(x, y)
}
g(x = 3)

or even

yEqualsX <- function(f) function(x, y = x) f(x, y)

yEqualsX(f)(x = 3)

These are a lot like currying, but aren't currying, so they may be 
acceptable to you.  Personally I'd choose the first one.

Duncan Murdoch