# itertools

A collection of Iterator functions inspired by Python's `itertools` module,
adapted to the conventions of Go.

| Python | Go | Description |
| --- | --- | --- |
| `count(start=0)` | `Count[N Number](start N) iter.Seq[N]` | Yield numbers from `start`, incrementing by 1, without end. |
| `count(start=0, step=1)` | `CountStep[N Number](start, step N) iter.Seq[N]` | Yield numbers from `start`, incrementing by `step`, without end. |
| `repeat(object)` | `RepeatForever[T any](v T) iter.Seq[T]` | Yield the same value over and over, without end. |
| `repeat(object, times)` | `Repeat[T any](v T, times int) iter.Seq[T]` | Yield the same value `times` times, then stop. |
| `islice(iterable, stop)` | `Take[T any](n int, seq iter.Seq[T]) iter.Seq[T]` | Yield the first `n` items of the source sequence, then stop. |
| `cycle(iterable)` | `Cycle[T any](seq iter.Seq[T]) iter.Seq[T]` | Yield the values of `seq`, saving a copy, then repeat them endlessly. |
| `chain(*iterables)` | `Chain[T any](seqs ...iter.Seq[T]) iter.Seq[T]` | Yield the values of each sequence in turn, exhausting one before starting the next. |
| `filter(predicate, iterable)` | `Filter[T any](predicate func(T) bool, seq iter.Seq[T]) iter.Seq[T]` | Yield only the values of `seq` for which `predicate` returns true. |


## References

* `slices.Filter` was rejected in 2021: [proposal: slices: new package to provide generic slice functions (discussion)](https://github.com/golang/go/discussions/47203#discussioncomment-1034432) (comment: Update, July 21 2021). Wrapping up the discussion, Russ Cox wrote: "Deleted Map, Filter, Reduce (probably better as part of a more comprehensive streams API somewhere else)". This package is a contribution to that future streams API.
* Rob Pike killed `slices.Filter` again in 2023: [Proposal: add generic Filter to slices package](https://github.com/golang/go/issues/58014)