## simple Message Parsing Interface

.ess_mpi_send <- function(head, ...){
    dots <- lapply(list(...), function(el) {
        if (is.null(el)) "nil"
        else if (is.logical(el)) {if (el) "t" else "nil"}
        else as.character(el)
    })
    payload <- paste(dots, collapse = "")
    cat(sprintf("_%s%s\\", head, payload))
}

.ess_mpi_message <- function(msg){
    .ess_mpi_send("message", msg)
}

.ess_mpi_y_or_n <- function(prompt, callback = NULL){
    .ess_mpi_send("y-or-n", prompt, callback)
}

.ess_mpi_eval <- function(expr, callback = NULL){
    .ess_mpi_send("eval", expr, callback)
}

.ess_mpi_error <- function(msg) {
    .ess_mpi_send("error", msg)
}