Package 'defer'

Run a block of code, collecting deferrable errors

Description

Run a block of code, collecting any deferrable_error calls that occur. Ordinary errors will be thrown immediately.

Usage

defer_errors(expr, handler = stop)

Arguments

expr	An expression to evaluate
handler	The final handler for the deferred errors. The default is stop which will raise the collected error. Alternatively, use return to return the error

Details

The error object will contain an element errors with the deferred errors, each of which will contain elements message, call (the call that precedes deferrable_error and calls which contains the "interesting" part of the stack trace (i.e., only calls below the defer_errors infrastructure).

Examples

check_positive <- function(x) {
  if (x < 0) {
    deferrable_error(paste("got a negative number:", x))
  }
}
err <- tryCatch(
  defer::defer_errors({
    check_positive(0)
    check_positive(-1)
    check_positive(-2)
  }),
  error = identity)
err

# Directly return the error:
err <- defer::defer_errors({
  check_positive(0)
  check_positive(-1)
  check_positive(-2)
}, handler = return)

# Stack traces are included to improve downstream reporting:
f <- function(x) {
  g(x)
}
g <- function(x) {
  check_positive(x)
}
err <- defer_errors({
  f(0)
  f(-1)
  f(-2)
}, handler = return)
err$errors[[1]]$calls

---

Create a deferrable error

Description

Create an error that will stop immediately, or can be continued from.

Usage

deferrable_error(message)

Arguments

message

The error message

Examples

# Deferrable errors will throw immediately if no suitable calling
# handlers are established:
tryCatch(
  deferrable_error("my error"),
  error = identity)

# Create a deferrable error and continue from it, using
# withCallingHandlers:
value <- withCallingHandlers({
   x <- 1
   defer::deferrable_error("a deferrable error")
   x * 2
 },
 deferrable_error = function(e)
   invokeRestart("continue_deferrable_error"))

---

Flush deferred errors

Description

Within a defer_errors block, flush any deferred errors, turning them into realised errors. If no deferrable errors have occurred, this function has no effect.

Usage

deferred_errors_flush()

Examples

check_positive <- function(x) {
  if (x < 0) {
    deferrable_error(paste("got a negative number:", x))
  }
}
err <- tryCatch(
  defer::defer_errors({
    check_positive(-1)
    defer::deferred_errors_flush()
    check_positive(-2)
  }),
  error = identity)
err

---