This package is a translation of the python itertools module. It includes all the usual suspects except for the cartesian product and permutation operators. All iterators are chan interface{} which allows some type ambiguity for these generic functions. It would be completely ok, however, to reproduce these functions in your package for your type-specific iterators such as chan MyStruct. I did this mostly as a thought exercise on converting python generators to Go.

Full documentation is available on godoc.

• Count(i) - Infinite count from i
• Cycle(iter) - Infinite cycling of iter (requires memory)
• Repeat(element [, n]) - Repeat element n times (or infinitely)

• New(elements ...) - Create from interface{} elements
• Int32(elements ...) - Create from int32 elements
• Int64(elements ...) - Create from int64 elements
• Uint(elements ...) - Create from uint elements
• Uint32(elements ...) - Create from uint32 elements
• Uint64(elements ...) - Create from uint64 elements
• Float32(elements ...) - Create from float32 elements
• Float64(elements ...) - Create from float64 elements

• Reduce(iter, reducer, memo) - Reduce (or Foldl) across the iterator.
• List(iter) - Create a list from the iterator

• Chain(iters...) - Chain together multiple iterators
• DropWhile(predicate, iter) - Drop elements until predicate(el) == false
• TakeWhile(predicate, iter) - Take elements until predicate(el) == false
• Filter(predicate, iter) - Filter out elements when predicate(el) == false
• FilterFalse(predicate, iter) - Filter out elements when predicate(el) == true
• Slice(iter, start[, stop[, step]]) - Drop elements until the start (0-based index). Stop upon stop (exclusive) unless not given. Step is 1 unless given.

• Map(mapper func(interface{}) interface{}, iter) - Map each element to mapper(el)
• MultiMap(multiMapper func(interface{}...)interface{}, iters...) - Map all the iterators as variadic arguments to multiMaper(elements...). Stop on shortest iterator.
• MultiMapLongest(multiMapper func(interface{}...)interface{}, iters...) - Same as MultiMap except stop on longest iterator. Shorter iterators are filled with nil after they are exhausted.
• Starmap(multiMapper func(interface{}...)interface{}, iter) - If iter is an iterator of []interface{}, then expand it into the multiMapper.
• Zip(iters...) - Zip multiple iterators together
• ZipLongest(iters...) - Zip multiple iterators together. Take the longest. Shorter ones are appended with nil.
• Tee(iter, n) - Split an iterator into n equal versions.
• Tee2(iter) - Split an iterator into two equal versions

BenchmarkFilter   200000         41188 ns/op
BenchmarkNoFilter    5000000           640 ns/op
BenchmarkMap       10000        108577 ns/op
BenchmarkNoMap  10000000           321 ns/op
BenchmarkReduce  1000000          1962 ns/op
BenchmarkNoReduce   100000000           22.0 ns/op

Clearly this package is much slower than doing just the original operations. However, all large systems inevitably involve abstractions and layers of indirection which are convinient while adding overhead. A system designer should think carefully before choosing one over the other. To be clear, this package was written as a thought experiment, and while usable, might represent a pattern to be rewritten using your types in your project to save the cost of typecasting overhead.

Thanks to damienklinnert for the benchmarks.

Copyright (c) 2013 Jon Eisen

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