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#' Set Macaulay2 ring
#'
#' \code{use_ring()} sets the default referent ring on the Macaulay2
#' side using the \code{use} function.
#'
#' @param ring a \code{m2_ring} (see [ring()]),
#' \code{m2_ring_pointer} (see [ring.()]), or a character
#' string containing the name of a ring in Macaulay2
#' @name use_ring
#' @examples
#'
#' \dontrun{ requires Macaulay2
#'
#'
#' ##### basic usage
#' ########################################
#'
#' ring("x", coefring = "QQ")
#' factor_poly("x^4 + 1")
#'
#' QQtxyz <- ring("t","x","y","z", coefring = "QQ")
#' gb("t^4 - x", "t^3 - y", "t^2 - z")
#'
#' ring("x", "y", "z", "t", coefring = "QQ")
#' gb("t^4 - x", "t^3 - y", "t^2 - z")
#'
#' use_ring(QQtxyz)
#' gb("t^4 - x", "t^3 - y", "t^2 - z")
#'
#' }
#' @export
#' @rdname use_ring
use_ring <- function(ring) {
# arg check
stopifnot(is.m2_polynomialring(ring) || is.m2_polynomialring_pointer(ring) || is.character(ring))
# construct code
if (is.m2(ring)) {
m2_code <- sprintf("use %s", m2_name(ring))
} else {
m2_code <- sprintf("use %s", ring)
}
# run m2
out <- m2.(m2_code)
# return
invisible(out)
}
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