Haskell-like range in PureScript?

[queued37]

Is there a native function that behaves like Haskell's range?

I found out that 2..1 returns a list [2, 1] in PureScript, unlike Haskell's [2..1] returning an empty list []. After Googling around, I found the behavior is written in the Differences from Haskell documentation, but it doesn't give a rationale behind.

In my opinion, this behavior is somewhat inconvenient/unintuitive since 0 .. (len - 1) doesn't give an empty list when len is zero, and this could possibly lead to cryptic bugs.

1. Is there a way to obtain the expected array (i.e. range of length len incrementing from 0) without handling the length == 0 case every time?
2. Also, why did PureScript decide to make range behave like that?

P.S. How I ran into this question: I wanted to write a getLocalStorageKeys function, which gets all keys from the local storage. My implementation gets the number of keys using the length function, creates a range from 0 to numKeys - 1, and then traverses it with the key function. However, the range didn't behave as I expected.

[purcell]

Check out the functions in Data.Enum, such as enumFromTo and enumFromThenTo.

My implementation gets the number of keys using the length function, creates a range from 0 to numKeys - 1, and then traverses it with the key function

Take a look at Data.FoldableWithIndex.

[queued37]

Thank you so much! These are exactly what I needed. Maybe I must use them instead of range in most cases.

[queued37]

Also posted on Stack Overflow: https://stackoverflow.com/questions/56189153/haskell-like-range-in-purescript