Stream: beginners

Topic: ✔ Populating a Dict via List.walk (in the REPL)

view this post on Zulip Hristo (Mar 10 2024 at 10:48):

With the intention of performing much more complex dictionary updates (involving Dict.update), I'm currently stuck on the following:

list = ["a", "b", "c", "d", "e", "f"]

{- ["a", "b", "c", "d", "e", "f"] : List Str-}

d = List.walkWithIndex list (Dict.empty {}) \state, elem, i -> Dict.insert state elem i

{- @Dict { buckets: [{ dataIndex: 5, distAndFingerprint: 466 }, { dataIndex: 3, distAndFingerprint: 721 }, { dataIndex: 4, distAndFingerprint: 977 }, { dataIndex: 1, distAndFingerprint: 1231 }, { dataIndex: 2, distAndFingerprint: 1487 }, { dataIndex: 0, distAndFingerprint: 1634 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0,
distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }], data: [("a", 0), ("b", 1), ("c", 2), ("d", 3), ("e", 4), ("f", 5)], maxBucketCapacity: 12, maxLoadFactor: 0.8, shifts: 60 } : Dict Str U64 -}

Dict.get d "c"

{- Err KeyNotFound : Result U64 [KeyNotFound] -}

{- Tried alternatively with the following, but the effect was equivalent:
d = List.walkWithIndex list (Dict.empty {}) \state, elem, i -> state |> Dict.insert elem i -}

whereas

d =
     Dict.empty {}
     |> Dict.insert "a" 0
     |> Dict.insert "b" 1
     |> Dict.insert "c" 2
     |> Dict.insert "d" 3
     |> Dict.insert "e" 4
     |> Dict.insert "f" 5

{- @Dict { buckets: [{ dataIndex: 3, distAndFingerprint: 497 }, { dataIndex: 4, distAndFingerprint: 753 }, { dataIndex: 5, distAndFingerprint: 1008 }, { dataIndex: 2, distAndFingerprint: 1263 }, { dataIndex: 1, distAndFingerprint: 1518 }, { dataIndex: 0, distAndFingerprint: 1551 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }, { dataIndex: 0, distAndFingerprint: 0 }], data: [("a", 0), ("b", 1), ("c", 2), ("d", 3), ("e", 4), ("f", 5)], maxBucketCapacity: 12, maxLoadFactor: 0.8, shifts: 60 } : Dict Str (Num *) -}

Dict.get d "c"

{- Ok 2 : Result (Num *) [KeyNotFound] -}

Please, note that equivalent behaviour is observed when utilising List.walk as well.

Could somebody please point me to where the issue in my code is?
Thank you for your time!

view this post on Zulip Luke Boswell (Mar 10 2024 at 11:05):

Looks like a bug to me. I think these should produce the same thing.

view this post on Zulip Hristo (Mar 10 2024 at 11:09):

Thank you for confirming!

Yes, the data portions of those are indeed the same, and I'd expect equivalent behaviour as well ( I just wasn't sure if I was using the correct syntax, even though I tried multiple variations of positioning parentheses).

I've been getting some odd functionality when trying to utilise Dict.update and (independently) when using List as the state.

I'll raise a GitHub ticket about this when I get a chance.

view this post on Zulip Notification Bot (Mar 10 2024 at 18:13):

Hristo has marked this topic as resolved.

view this post on Zulip Hristo (Mar 10 2024 at 19:14):

Just adding a bit more context - this only occurs in Roc's REPL.
In traditionally compiled Roc, this hasn't been reproduced.

view this post on Zulip Brendan Hansknecht (Mar 10 2024 at 19:42):

Cool. So bug on the dev backend

Last updated: Jul 26 2025 at 12:14 UTC