Alternative R compose function

compose2.R

library(purrr)

compose2 <- function (...)  {
  fs <- lapply(list(...), match.fun)
  n <- length(fs)
  last <- fs[[n]]
  rest <- fs[-n]
  newf <- function(...) {
    cl <- match.call()
    cl[[1L]] <- last
    out <- eval(cl)
    for (f in rev(rest)) {
      out <- f(out)
    }
    out
  }
  formals(newf) <- formals(last)
  newf
}

#not_null <- compose2(`!`, is.null)
#not_null(4)
#not_null(NULL)


add1 <- function(x) x + 1
compose(add1, add1)(8)
formals(add1)

Unlike purrr::compose, the returned function has the same formals as the last (innermost) function. This is useful for autocompletion and documentation of the new function. However, since primitives don't have formals, this isn't completely general.