withCallingHandlers() और पुनःआरंभ

# Without muffleWarning: warning still shows after handler
withCallingHandlers({
  warning('test')
}, warning = function(w) {
  cat('Handler ran\n')
  # no muffleWarning: default handler still fires
})

withCallingHandlers({
  message('Progress: 50%')
  message('Progress: 100%')
}, message = function(m) {
  cat('[LOG]', trimws(m$message), '\n')
  invokeRestart('muffleMessage')
})

warnings_log <- character(0)
result <- withCallingHandlers({
  x <- log(-1)
  y <- sqrt(-4)
  c(x, y)
}, warning = function(w) {
  warnings_log <<- c(warnings_log, w$message)
  invokeRestart('muffleWarning')
})
cat('Warnings logged:', length(warnings_log), '\n')
cat(warnings_log, sep = '\n')

# withRestarts() offers named recovery options
divide_safe <- function(x, y) {
  withRestarts(
    {
      if (y == 0) stop('division by zero')
      x / y
    },
    use_zero = function() 0,
    use_na   = function() NA
  )
}
# A handler can pick a restart
withCallingHandlers(
  divide_safe(10, 0),
  error = function(e) invokeRestart('use_zero')
)

n_warnings <- 0L
result <- withCallingHandlers(
  tryCatch(log(-1), warning = function(w) -999),
  warning = function(w) {
    n_warnings <<- n_warnings + 1L
    cat('Logged warning #', n_warnings, '\n')
  }
)
cat('Result:', result, '\n')

my_error <- function(msg, data = NULL) {
  structure(
    class = c('my_error', 'error', 'condition'),
    list(message = msg, data = data)
  )
}
tryCatch(
  stop(my_error('custom error', data = 42)),
  my_error = function(e) cat('Custom handler, data=', e$data, '\n'),
  error    = function(e) cat('Generic handler\n')
)

# withCallingHandlers: observe all, continue
withCallingHandlers(
  for (x in c(4, -1, 9, -4)) cat(suppressWarnings(sqrt(x)), ''),
  warning = function(w) cat('[warn]', '')
)
cat('\n')

# Demonstrate: withCallingHandlers handler can see full stack
f <- function() {
  withCallingHandlers(
    g(),
    warning = function(w) {
      cat('Caught in f, stack length:', sys.nframe(), '\n')
      invokeRestart('muffleWarning')
    }
  )
}
g <- function() warning('from g')
f()

# Suppress only NaN warnings, not others
suppress_nan_warn <- function(expr) {
  withCallingHandlers(expr, warning = function(w) {
    if (grepl('NaN', conditionMessage(w)))
      invokeRestart('muffleWarning')
  })
}
suppress_nan_warn(log(-1))   # NaN warning suppressed
tryCatch(
  suppress_nan_warn(warning('other issue')),
  warning = function(w) cat('Other warning kept:', w$message, '\n')
)

log_vec <- character(0)
withCallingHandlers({
  message('start')
  warning('low memory')
  message('end')
}, message = function(m) {
  log_vec <<- c(log_vec, paste('MSG:', trimws(m$message)))
  invokeRestart('muffleMessage')
}, warning = function(w) {
  log_vec <<- c(log_vec, paste('WARN:', w$message))
  invokeRestart('muffleWarning')
})
cat(log_vec, sep = '\n')