How do people quickly check that they have a non-empty list of X?

(not (null? xs))

Where xs is my list

There’s also (andmap (const #t) xs), but that’s a little less clear

I seee

I was just wondering because all? seems to return true if list is empty

Okay, that actually does make sense and I screwed up in the exact same way here

I should’ve used ormap above

The thing is, it’s true the every value of the empty list satisfies e.g. odd? or boolean?

What explains the first part or vs and?

like

how did you know ormap returns false for empty list

because intuitively, I woudl’ve thought it was flip flopped

Because I want the property that (ormap p (cons x xs)) is (or (p x) (ormap p xs))

Does it make sense that that should be true?

kind of -_-a

Well, what should ormap do? Can you implement it as a recursive function/loop?

I would imagine (ormap fn lst) means to map boolean function to list, and then if there’s a single true, return true

Right!

AHH

yes

Are there any elements of the empty list for which fn would return true?

it makes sense

:)

the symmetry to andmap makes sense

thanks!

No problem. Sorry for getting it wrong in my initial explanation haha

ahh no wait

ormap isn’t what I’m looking for

like

(ormap integers? (1 2 'meow')

would return true

So do you want andmap but false for the empty list?

yeah

Why do you want to reject the empty list?

Because I feel for a series of numerical operations

You would propogate an empty list down

like you’re checking if you have a non-empty list of only integers

and you do an operation assuming you only have non-empty lists

So what operation are you doing which doesn’t make sense for an empty list? If you’re sure that you don’t want it you can just check that it’s nonempty before doing your series of numerical operations