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# This is based on code that was contributed by Hadley Wickham
hasNext.ihasNext <- function(obj, ...) {
obj$hasNext()
}
ihasNext <- function(iterable) {
it <- iter(iterable)
if (inherits(it, 'ihasNext')) {
it
} else {
cache <- NULL
hasnext <- NA
nextEl <- function() {
if (! hasNx()) {
stop('StopIteration', call.=FALSE)
}
hasnext <<- NA
cache
}
hasNx <- function() {
if (is.na(hasnext)) {
tryCatch({
cache <<- nextElem(it)
hasnext <<- TRUE
},
error=function(e) {
if (identical(conditionMessage(e), 'StopIteration')) {
hasnext <<- FALSE
} else {
stop(e)
}
})
}
hasnext
}
obj <- list(nextElem=nextEl, hasNext=hasNx)
class(obj) <- c('ihasNext', 'abstractiter', 'iter')
obj
}
}
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