An alist function that works with '...' objects.

alist2.R

#' Create an \code{alist}.
#'
#' An alternative to \code{base::alist} that works with \code{...} objects
#' inside a function.
#'
#' An \code{alist} is a list containing possibly unevaluated arguments. The
#' standard implementation of \code{alist} does not work with \code{...} objects
#' inside a function, but this one does. Uses of this function includes partial
#' function application and easier handling of generics that make use of
#' \code{...}, for instance \code{plot}.
#'
#' @param ... objects, possibly named. Can be passed from the calling function.
#' @return A \code{list} with potentially unevaluated arguments.
#' @examples
#'    # Make a wrapper around stats::glm that always calls gamma regression.
#'
#'    gr = function(...) {
#'      dots = alist2(...)
#'      dots$family = quote(Gamma)
#'      do.call("glm", dots)
#'    }
#'
#'    gr_list = function(...) {
#'      dots = list(...)
#'      dots$family = quote(Gamma)
#'      do.call("glm", dots)
#'    }
#'
#'    gr_alist = function(...) {
#'      dots = alist(...)
#'      dots$family = quote(Gamma)
#'      do.call("glm", dots)
#'    }
#'
#'    # Only 'gr' returns the intended output.
#'    gr(formula = disp ~ cyl + mpg, data = mtcars)
#'    gr_list(formula = disp ~ cyl + mpg, data = mtcars)
#'    gr_alist(formula = disp ~ cyl + mpg, data = mtcars)
#'
#'
#'    # Make a thin wrapper over plot that always plots lines instead of points
#'    # as the default option.
#'
#'    lplot = function(...) {
#'     dots = alist2(...)
#'     if(is.null(dots$type)) dots$type = "l"
#'     do.call("plot", dots)
#'    }
#'
#'    lplot_list = function(...) {
#'     dots = list(...)
#'     if(is.null(dots$type)) dots$type = "l"
#'     do.call("plot", dots)
#'    }
#'
#'    lplot_alist = function(...) {
#'     dots = alist(...)
#'     if(is.null(dots$type)) dots$type = "l"
#'     do.call("plot", dots)
#'    }
#'
#'    z = sort(rnorm(10))
#'    w = sort(rnorm(10))
#'
#'    # Only lplot yields the intended plot.
#'    lplot(z, w, type = "b")
#'    lplot_list(z, w, type = "b")
#'    lplot_alist(z, w, type = "b")

alist2 = function(...) as.list(substitute(tmp(...)))[-1]

## Testing the alist2 function.
identical(alist2(a = , b = , x = 1, 2, 3, 4),
           alist(a = , b = , x = 1, 2, 3, 4))

identical(alist2(1, a = 1:10, b = , 1, 2),
           alist(1, a = 1:10, b = , 1, 2))

identical(alist2(1, 2),
           alist(1, 2))

identical(alist2(1, 2, a = ),
           alist(1, 2, a = ))

identical(alist2(a = , b = ),
           alist(a = , b = ))

identical(alist2(a = 1:10, b = 1:10),
           alist(a = 1:10, b = 1:10))