##
##  f i g u r e . r  Figure (Matlab Style)
##


figure <- function(figno, title = "") {
    if (missing(figno)) figno <- NULL
    else {
        if (!is.numeric(figno) || length(figno) != 1 || floor(figno) != ceiling(figno))
            stop("The figure handle must be a whole number.")
    }

    if (!is.null(figno)) {
        if (figno == 1 || figno == -1) {
            stop("Device 1 is the null device; cannot be opened or closed.")
        } else if (figno == 0) {
            stop("Requested figure handle 0 is in use by another object.")
        }
    }

    if (.Platform$OS.type == "unix") {
        if (.Platform$GUI == "AQUA") win <- quartz
        else if (.Platform$GUI == "X11") win <- X11
        else
            stop("Unknown platform GUI for Unix platform type.")
    } else if (.Platform$OS.type == "Linux") {
        win <- X11
    } else if (.Platform$OS.type == "windows") {
        win <- windows
    } else
        stop(paste("Unknown platform type:", .Platform$OS.type))

    if (is.null(figno)) {
        win()
    } else {
        devl <- dev.list()
        if (abs(figno) %in% devl) {
            if (figno > 0) dev.set(figno)
            else           dev.off(-figno)
        } else {
            cat("Device", figno, "is not an open device. List of devices:\n")
            return(devl)
        }
    }
    invisible()
}

##  Comment:
#   dev.new() may be platform independent.
#