Evaluate an expression, restarting on error

A pair of functions paralleling eval() and evalq() that make multiple attempts at evaluating an expression, retrying on error up to a specified number of attempts, and optionally evaluating another expression before restarting.

persistEval(
  expr,
  retries = NVL(getOption("eval.retries"), 5),
  beforeRetry,
  envir = parent.frame(),
  enclos = if (is.list(envir) || is.pairlist(envir)) parent.frame() else baseenv(),
  verbose = FALSE
)

persistEvalQ(
  expr,
  retries = NVL(getOption("eval.retries"), 5),
  beforeRetry,
  envir = parent.frame(),
  enclos = if (is.list(envir) || is.pairlist(envir)) parent.frame() else baseenv(),
  verbose = FALSE
)

Arguments

expr

an expression to be retried; note the difference between eval() and evalq().

retries

number of retries to make; defaults to "eval.retries" option, or 5.

beforeRetry

if given, an expression that will be evaluated before each retry if the initial attempt fails; it is evaluated in the same environment and with the same quoting semantics as expr, but its errors are not handled.

envir, enclos

see eval().

verbose

Whether to output retries.

Value

Results of evaluating expr, including side-effects such as variable assignments, if successful in retries retries.

Note

If expr returns a "try-error" object (returned by try()), it will be treated as an error. This behavior may change in the future.

Examples

x <- 0
persistEvalQ({if((x<-x+1)<3) stop("x < 3") else x},
             beforeRetry = {cat("Will try incrementing...\n")})
#> Will try incrementing...
#> Will try incrementing...
#> [1] 3

x <- 0
e <- quote(if((x<-x+1)<3) stop("x < 3") else x)
persistEval(e,
            beforeRetry = quote(cat("Will try incrementing...\n")))
#> Will try incrementing...
#> Will try incrementing...
#> [1] 3