statnet.common (version 4.10.0)

persistEval: Evaluate an expression, restarting on error

Description

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.

Usage

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
)

Value

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

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.

Examples

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

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