Alter a function as a parameter before evaluating it in R?
- by Shane
Is there any way, given a function passed as a parameter, to alter its input parameter string before evaluating it?
Here's pseudo-code for what I'm hoping to achieve:
test.func <- function(a, b) {
# here I want to alter the b expression before evaluating it:
b(..., val1=a)
}
Given the function call passed to b, I want to add in a as another parameter without needing to always specify ... in the b call. So the output from this test.func call should be:
test.func(a="a", b=paste(1, 2))
"1" "2" "a"
Edit:
Another way I could see doing something like this would be if I could assign the additional parameter within the scope of the parent function (again, as pseudo-code); in this case a would be within the scope of t1 and hence t2, but not globally assigned:
t2 <- function(...) {
paste(a=a, ...)
}
t1 <- function(a, b) {
local( { a <<- a; b } )
}
t1(a="a", b=t2(1, 2))
This is somewhat akin to currying in that I'm nesting the parameter within the function itself.
Edit 2:
Just to add one more comment to this: I realize that one related approach could be to use "prototype-based programming" such that things would be inherited (which could be achieved with the proto package). But I was hoping for a easier way to simply alter the input parameters before evaluating in R.
