In brodieG/recsub: Recursive Quoted Language Expansion

knitr::opts_chunk$set(error=TRUE, comment=NA)
library(oshka)

Other Considerations

One drawback of the eval/bquote/.() pattern is that the actual objects inside .() are placed on the call stack. This is not an issue with symbols, but can be bothersome with data or functions. For example, in:

my_fun_inner <- function(x) {
  # ... bunch of code
  stop("end")
}
my_fun_outer <- function(x) {
  eval(bquote(.(my_fun)(.(x))), parent.frame())
}
my_fun_outer(mtcars)
traceback()

The entire deparsed function definition and data frame will be displayed in the traceback, which makes it difficult to see what is happening. A simple work-around is to use:

sapply(.traceback(), head, 1)
sapply(sys.calls(), head, 1)  # sys.calls is similarly affected

Versus `rlang`

oshka is simple in design and purpose. It exports a single function that substitutes expressions into other expressions. It hews closely to R semantics. rlang is more ambitious and more complex as a result. To use it you must learn new concepts and semantics.

One manifestation of the additional complexity in rlang is that you must unquote expressions to use them:

rlang.b <- quo(Species == 'virginica')
rlang.c <- quo(Sepal.Width > 3.6)
rlang.d <- quo(!!rlang.b & !!rlang.c)

dplyr::filter(iris, !!rlang.d)

As shown earlier, the expand version is more straightforward as it uses the standard quote function and does not require unquoting:

On the other hand, forwarding of NSE arguments to NSE functions is simpler in rlang due to environment capture feature of quosures:

rlang_virginica <- function(subset) {
  subset <- enquo(subset)
  dplyr::filter(iris, Species == 'virginica' & !!subset)
}

Because oshka does not capture environments, we must resort to the eval/bquote pattern:

oshka_virginica <- function(subset) {
  subset <- bquote(Species == 'virginica' & .(substitute(subset)))
  eval(bquote(.(subset2)(iris, .(subset))), parent.frame())
}