Rob Pike's repository 'filter'[0] contains implementations of map ("Apply"), filter ("Choose", I believe), and fold/reduce ("Reduce"). The code is an ugly mess, and the implementation shows that he probably hasn't used any of these
standard functions in other languages (see the weird permutations of 'filter' in apply.go, or my patch for his fold/reduce implementation[1]). The README is also quite arrogant, IMO.
> I wanted to see how hard it was to implement this sort of thing in Go, with as nice an API as I could manage. It wasn't hard.
> Having written it a couple of years ago, I haven't had occasion to use it once. Instead, I just use "for" loops.
> You shouldn't use it either.
[0]: https://github.com/robpike/filter/
[1]: https://github.com/robpike/filter/pull/1
> I wanted to see how hard it was to implement this sort of thing in Go, with as nice an API as I could manage. It wasn't hard.
> Having written it a couple of years ago, I haven't had occasion to use it once. Instead, I just use "for" loops.
> You shouldn't use it either.
[0]: https://github.com/robpike/filter/
[1]: https://github.com/robpike/filter/pull/1