util: Utilities for writing iterators

In itertools: Iterator Tools

Description

is.iterator indicates if an object is an iterator. end_iteration throws an exception to signal that there are no more values available in an iterator. iteration_has_ended tests an exception to see if it indicates that iteration has ended. new_iterator returns an iterator object.

Usage

is.iterator(x)
end_iteration()
iteration_has_ended(e)
new_iterator(nextElem, ...)

Arguments

x	any object.
e	a condition object.
nextElem	a function object that takes no arguments.
...	not currently used.

Examples

# Manually iterate using the iteration_has_ended function to help
it <- iter(1:3)
tryCatch({
  stopifnot(is.iterator(it))
  repeat {
    print(nextElem(it))
  }
},
error=function(e) {
  if (!iteration_has_ended(e)) {
    stop(e)
  }
})

itertools documentation built on May 2, 2019, 2:26 p.m.