Support for decorators

[lorenzwalthert]

For example like in Python. This would allow things like

# cache a function
@R.cache::cache()
slow_fun <- function() {
  ...
}

# parametrize tests with all combinations like pytetst
@testthat::cross(x = 1:2, y = 1:2) 
test_that('can create prod', {
  expect_equal(
    my_prod(x, y), 
    x * y
  )
})

[nfultz]

couple thoughts

1. the at sign is already taken for S4
2. In python, it only works with def and not lambda. R's function works closer to lambda.
3. You can already write "setter" functions eg how names()<- and class()<- work. They are not exactly the same, but could be used to do similar things.

[lorenzwalthert]

Thanks @nfultz. I know it's already taken for S4, but I think it would be still possible, since with S4, it's always within an expression as far as I know, e.g. x@y, and never @y, e.g. as the first token on a line. Right? There are symbols in R that have multiple meanings depending on the context, e.g. + as an infix operator for two arguments or as a sign.

[ColinFay]

Would you be ok with explaining this to someone not knowing Python and that doesn't know what decorators are? :)

[nfultz]

I think @ is a primitive so it's a special case. I guess if - can have a different meaning in prefix and infix form, there's no reason @ couldn't.

Another thought - R generally doesn't use significant whitespace like Python does, so not clear to me how it could know to apply a decorator to the next line.

@Colin Fay - decorators are syntax sugar for applying higher order functions. so instead of writing

a <- function(x) { ...}

a <- cache(a)

one would write

@cache
a <- function(x) { ... }

On Fri, Jan 28, 2022 at 8:29 AM Lorenz Walthert @.***> wrote:

Thanks @nfultz https://github.com/nfultz. I know it's already taken for S4, but I think it would be still possible, since with S4, it's always within an expression as far as I know, e.g. @.***, and never @y, e.g. as the first token on a line. Right?

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[HenrikBengtsson]

Potential related to this, is https://github.com/dirkschumacher/defmacro. It might provide a way to declare these this using R syntax.