How to represent a for loop

[samwaseda]

It's closely related to #24, but since it's getting pretty long, I open a new issue.

Let's talk about the following workflow:

def my_workflow(n):
    for ii in my_list(n):
        n = my_function(ii)
    return n

Now, following the logic from #24, there would be an edge from inputs.n to my_list, then my_list to my_function, finally my_function to output. Now, however, there are two significant differences:

1. The output of my_function is not the input of my_list, as my_list is evaluated only once when n is inserted
2. ii is not the output of my_list, but it's each element of the output of my_list.

So I'm feeling that maybe our edge representation is not good enough to cover the for loop. What do you think? @liamhuber

[liamhuber]

1. The output of my_function is not the input of my_list, as my_list is evaluated only once when n is inserted

Agreed, of course. The cyclicity against which you're contrasting was information explicitly carried in 'type': 'while', I wouldn't generally expect my_list to get called again or for my_function to be able to impact it.

2. ii is not the output of my_list, but it's each element of the output of my_list.

Analogously, I think this is what is carried by 'type': 'for'.

So I'm feeling that maybe our edge representation is not good enough to cover the for loop. What do you think? @liamhuber

I can't say the edge representation is necessarily optimal, but I do think in light of the above, it's sufficient: 'while' carries information to modify the edges to add cyclicity, 'for' carries information to modify the edges to access elements (and be directed to copies/re-invocations of the body node(s)).

[liamhuber]

I do rather start to worry that while all of this has the pro that we can write natural-ish python, it is only natural-ish.
We insist that all non-declarative actions be wrapped in functions, we support some but not all operations (here I think of zip, later unpacking **kwargs terrifies me, and we haven't handled operators (even simple + or ==) at all.

I'm not saying we should stop now or abandon this line of attack, I'm just saying my philosophical concern of whether it's easier to learn something new from scratch or unlearn parts of something you already know is starting to rear its ugly head again...