Ilya Shmygol (Apr 16 2025 at 12:42): Ilya Shmygol (Apr 16 2025 at 12:42):Another example of questionable behaviour in my opinion.
Here is a piece of code i had:
parse_template_recursive : List U8, List (Spec _) -> Result (List (Spec _)) [InvalidTemplate([MissingClosingBracket])]
parse_template_recursive = |template_codes, acc|
when split_first_segment(template_codes) is
Err(ListWasEmpty) -> Ok(acc)
Err(MissingClosingBracket) -> MissingClosingBracket |> InvalidTemplate |> Err
Ok({before : ['{', .. ,'}'], others}) -> crash("Not implemented yet")
Ok({before, others}) -> crash("Not implemented yet")
split_first_segment may currently return only 2 types of errors: ListWasEmpty and MissingClosingBracket, but in the feature may be extended with other errors. Should the pattern matcher be smart enough to understand this:
parse_template_recursive : List U8, List (Spec _) -> Result (List (Spec _)) [InvalidTemplate([MissingClosingBracket])]
parse_template_recursive = |template_codes, acc|
when split_first_segment(template_codes) is
Err(ListWasEmpty) -> Ok(acc)
Err(reason) -> reason |> InvalidTemplate |> Err
Ok({before : ['{', .. ,'}'], others}) -> crash("Not implemented yet")
Ok({before, others}) -> crash("Not implemented yet")
Because currently even if I do handle a case when ListWasEmpty has being thrown I still get an error:
TYPE MISMATCH
Something is off with the body of the
`parse_template_recursive` definition:
120│ parse_template_recursive : List U8, List (Spec _) -> Result (List (Spec _)) [InvalidTemplate([MissingClosingBracket])]
121│ parse_template_recursive = |template_codes, acc|
122│> when split_first_segment(template_codes) is
123│> Err(ListWasEmpty) -> Ok(acc)
124│> Err(reason) -> reason |> InvalidTemplate |> Err
125│> Ok({before : ['{', .. ,'}'], others}) -> crash("Not implemented yet")
126│> Ok({before, others}) -> crash("Not implemented yet")
This `when` expression produces:
[
Err [InvalidTemplate [
ListWasEmpty,
MissingClosingBracket,
]],
Ok (List (Match.Spec c)),
]
But the type annotation on
`parse_template_recursive` says it should be:
Result (List (Match.Spec c)) [InvalidTemplate [MissingClosingBracket]]
Should the pattern matcher be smart enough to understand this
Yes, it should be but it is quite limited at the moment. I'll make an issue.
Anton (Apr 16 2025 at 16:51): Brendan Hansknecht (Apr 16 2025 at 17:17):No this should not work
Brendan Hansknecht (Apr 16 2025 at 17:17):As much as it feels it should
Brendan Hansknecht (Apr 16 2025 at 17:17):Roc has no gradual typing
Brendan Hansknecht (Apr 16 2025 at 17:18):The type of reason is [ListWasEmpty, MissingClosingBracket]
Brendan Hansknecht (Apr 16 2025 at 17:19):Think of it like this. If you had an enum Color: [Red, Green, Blue]. Even if the function is guaranteed to return Blue, the type is still Color. The same thing is happening here
Brendan Hansknecht (Apr 16 2025 at 17:20):I know this has been discussed in the past, but I don't think there are any current plans to add gradual typing for tag unions.
Anton (Apr 16 2025 at 17:46):No this should not work
Yeah, I was doubting as well when I wrote up the issue. I'll close it.
Ilya Shmygol (Apr 16 2025 at 19:39):Got it, thanks.
Last updated: Jul 26 2025 at 12:14 UTC