Ian McLerran (Jun 16 2024 at 02:29): Ian McLerran (Jun 16 2024 at 02:29):So I came across a strange type inferencing issue today:
If I define a function which uses type variables, and then I write an expect statement which applies that function to multiple types, I get errors in the earlier applications of the function, complaining that they do not match the later applications.
However if I split my expects into a separate Test.roc module, I have no problem applying the function using multiple types.
So for example:
reduceListRight : List a, (a, a -> a) -> Result a [ListWasEmpty]
expect reduceListRight [] Num.add == Err ListWasEmpty
expect reduceListRight [5] Num.add == Ok 5
expect reduceListRight ["1", "2", "3"] Str.concat == Ok "321"
Produces the following errors:
── TYPE MISMATCH in Reduce.roc ─────────────────────────────────────────────────
This 1st argument to reduceListRight has an unexpected type:
24│ expect reduceListRight [5] Num.add == Ok 5
^^^
The argument is a list of type:
List (Num *)
But reduceListRight needs its 1st argument to be:
List Str
── TYPE MISMATCH in Reduce.roc ─────────────────────────────────────────────────
This 2nd argument to reduceListRight has an unexpected type:
24│ expect reduceListRight [5] Num.add == Ok 5
^^^^^^^
This add value is a:
Num a, Num a -> Num a
But reduceListRight needs its 2nd argument to be:
Str, Str -> Str
── TYPE MISMATCH in Reduce.roc ─────────────────────────────────────────────────
This 2nd argument to == has an unexpected type:
24│ expect reduceListRight [5] Num.add == Ok 5
^^^^
This Ok tag application has the type:
[Ok (Num *), …]
But == needs its 2nd argument to be:
[Ok Str, …]
I think your missing part of the module here. The listReduceRight is not the same as reduceListRight.
Ian McLerran (Jun 16 2024 at 03:52):Oh... haha! Partial copy/pasta, partial re-typing my code lol.
Ian McLerran (Jun 16 2024 at 03:56):(I fixed the mis-type)
Brendan Hansknecht (Jun 16 2024 at 05:10):And this is specific to expect? Doesn't happen with regular use?
Ian McLerran (Jun 16 2024 at 05:39):Thats a great question. I'm haven't actually tried calling the function from within the module except inside expect. Its a module in a package, not a application, but I can see if it passes roc check.
Ian McLerran (Jun 16 2024 at 05:40):Or maybe better yet, write a function which calls reduceListRight with a couple different types, and do an expect on that function...
Last updated: Jul 26 2025 at 12:14 UTC