R/except.R

In infix: Basic Infix Binary Operators

#' @name except
#' @aliases tryExcept
#' @aliases %except%
#'
#' @title Simple Error Handling
#'
#' @description Use this method to handle errors. The function evaluates an expression,
#'     and if it raises an error then evaluates a second expression.
#'
#' @details \code{tryExcept} is a wrapper around \code{\link[base]{tryCatch}},
#'     but it allows you to evaluate an expression \code{except} when an error occurs to
#'     the first expression argument \code{expr}. Note that, if \code{expr} raises
#'     an error, the code evaluated before the error will be in use.
#' @param expr Expression to be evaluated.
#' @param except Expression to be evaluated if \code{expr} raises an error. By default it is
#'     an empty expression.
#' @param error Handler function for an \code{error} condition occurred during the evaluation
#'     of \code{expr}. It's output is not used, as the output in case of an error is the
#'     evaluation of \code{except}. By default it is an empty function.
#' @examples
#' # No errors are raised
#' tryExcept(stop())
#'
#' # If 'expr' has no errors
#' tryExcept({
#'   foo <- "foo"
#' }, except = {
#'   foo <- "foo bar"
#' })
#' print(foo) # "foo"
#'
#' # If 'expr' has an error
#' tryExcept({
#'   foo <- "foo"
#'   stop()
#' }, except = {
#'   foo <- "foo bar"
#' })
#' print(foo) # "foo bar"
#'
#' # Running it with the infix operator
#' {foo <- "foo"} %except% {foo <- "foo bar"}
#' print(foo) # "foo"
#'
#' { foo <- "foo"
#'   stop()
#' } %except% {
#'   foo <- "foo bar"
#' }
#' print(foo) # "foo bar"
#' @export
tryExcept <- function(expr, except = {}, error = function(e){})
{
  tryCatch(return(expr), error = error)
  invisible(except)
}

#' @rdname except
#' @export
`%except%` <- function(expr, except) tryExcept(expr, except)