Utility function to try and fail with grace.

Inspired from one of Hadley's functions (in plyr or something?)

failWith(
  default = NULL,
  expr,
  frame = parent.frame(),
  message = geterrmessage(),
  silent = FALSE,
  file = stderr()
)

Arguments

default: the value to return if expr fails
expr: the expression to take a shot at
frame: the frame to evaluate the expression in
message: the error message to display if expr fails. Deafults to base::geterrmessage()
silent: if TRUE, sends the error message to msg()
file: where msg sends the message

the result of expr if successful, otherwise default value.

# look, this doesn't throw an error, it just returns NULL
x <- failWith(NULL, stop("no error, just NULL"), silent = TRUE)