Stream: helpdesk (published)

Topic: local scope assignment comprehension


view this post on Zulip Filippos Christou (Apr 13 2022 at 13:19):

Something that has been haunting me for some time. I don't know if it's a gripe, a feature request or just lack of knowledge but:
There are cases where I want to do a complicated comprehension.
In these cases I just wish there was a way to make the expression more readable by having some local assignments.

example time

mysuperlongandcomplicateddataretrieval(x) = x+1
v = [0,1,2,3]

# so normally one would do:
com = [mysuperlongandcomplicateddataretrieval(x) >= 0 ? mysuperlongandcomplicateddataretrieval(x) : mysuperlongandcomplicateddataretrieval(x)-1 for x in v]

# what I would like to do is:
com = [y >= 0 ? y : y-1  for x in v for y=mysuperlongandcomplicateddataretrieval(x)]

you are probably wondering "Dude, that works!" but please have some fantasy and imagine that my list has non iteratable elements!
Normally I default doing something like this:

# iterate a single element list
com = [y >= 0 ? y : y-1 for x in v for y=[mysuperlongandcomplicateddataretrieval(x)]]

But it feels kind of hacky. I don't want to iterate, I just want to make an assignment.

view this post on Zulip Sebastian Pfitzner (Apr 13 2022 at 13:25):

com = [
    let y = mysuperlongandcomplicateddataretrieval(x)
        y >= 0 ? y : y-1
    end for x in v
]

view this post on Zulip Filippos Christou (Apr 13 2022 at 13:41):

That's an interesting one but would prefer if it was an oneliner.. which get me thinking; how come there is still not a @let or @begin macro. Then one could do:

com = [@let(y = mysuperlongandcomplicateddataretrieval(x), y >= 0 ? y : y-1) for x in v]

I guess this could lead to many parsing problems..

view this post on Zulip Sebastian Pfitzner (Apr 13 2022 at 13:44):

[let y = mysuperlongandcomplicateddataretrieval(x); y >= 0 ? y : y-1; end for x in v]

then

view this post on Zulip Filippos Christou (Apr 13 2022 at 13:51):

yes, I considered it but the end term in the middle of the comprehension can be confusing, which is why I though of a macro use case.


Last updated: Nov 22 2024 at 04:41 UTC