Fix join pipe function

[akshayphilar]

No description provided.

[renancunha]

I don't know exactly the purpose of this issue, but I'll describe a situation that I found using the join pipe and that deserves some discussion about it.

Generally, all shublang functions are executed through the iterable that they receive. But the join pipe is executed joining the iterable by a string. I think that instead of joining the iterable, it should apply the join operation on every item of the iterable.

In other words, instead of having the join function like this:

def join(iterable, separator=", "):
    return separator.join(builtins.map(str, iterable))

we should have:

def join(iterable, separator=", "):
    return (separator.join(builtins.map(str, x)) for x in iterable)

I came to this analyzing the following situation:

• Every time that I get data from a previous pipe like jmespath, I need to add a first, before using the join pipe. Another problem with the current approach is that they are returning a string, instead of an iterable. I think that we should be careful with the grammar in situations like this, to keep the shublang terse.

What do you think about it?
cc @BurnzZ @akshayphilar

[akshayphilar]

@renancunha you have captured the intent of this issue. Agree, join needs to be brought in line with other pipe functions as you have described above