Concat map

[matiboy]

• tests inspired by RxJS
• implementation from concat_map implementation or equivalent? #581 iyz91 's code
• documentation inspired by RxJS

[coveralls]

Coverage: 93.396% (+0.02%) from 93.375% when pulling c2ad7fe on matiboy:concat-map into 21ba043 on ReactiveX:master.

[dbrattli]

@matiboy Thanks for adding this. Looks great!

[dbrattli]

One thing I suddenly realized is that we might not need the _concat_map file if we make the composition inside __init__.py e.g:

return compose(map(project), merge(max_concurrent=1))

[matiboy]

One thing I suddenly realized is that we might not need the _concat_map file if we make the composition inside __init__.py e.g:

return compose(map(project), merge(max_concurrent=1))

Sorry mis-read initially and kept the "verbose" definition. But yes, beautiful one-liner.

[dbrattli]

Looks great. PS: another change we want to do is to borrow the curry_flip function from the Expression library to simplify all the operator implementations by removing all the nested functions. Take a look at https://github.com/cognitedata/Expression/blob/main/expression/collections/block.py#L602 Thus you can put source back as the first parameter, and curry-flip will move it as the last parameter curried (returning a function that takes it as the parameter). I can open an issue to discuss this more.