Alexander McLin (Feb 02 2023 at 21:41): Alexander McLin (Feb 02 2023 at 21:41):I thought I'd add here some examples of repl interactions that I found surprising and would like to understand them better.
When I enter 1 in the repl, I get back 1 : Num * # val1
I next enter 2, I get back 2 : Num * #val2
so far so good, nothing unusual.
I next enter val3 = 3 in the repl which gives back 3 : Num * #val3 as expected
I then enter 4 which gives me 4 : Num * #val3 yet typing in val3 still gives me back 3
Obviously the repl doesn't recognize that I already defined val3, clearly it's a bug, nothing really surprising. Not sure if it's already been noticed before?
Another example that seem to be a bug to me but maybe it's not?
If I enter a type declaration and definitionx : F32 then x = 5 really any type would work, it doesn't matter.
Then I enter \x -> x I get back a type of * -> F32 which seems odd to me. It suggests that the type checker has taken into account the x variable I already defined earlier when inferring \x -> x's type but the x in the lambda is just the formal parameter's name, and the x in the lambda's body is bound to the formal parameter. It shouldn't have anything to do with the top-level x variable right?
Indeed if I enter \y -> y where y doesn't already exist as a top-level variable, I get back a -> a as expected or \z -> z + 1 gives me Num a -> Num a but \x -> x + 1 or \x -> x gives me * -> F32 which I found surprising. It doesn't seem like it's doing the right thing here?
Folkert de Vries (Feb 02 2023 at 21:45):for that last problem: we don't allow shadowing, but it looks like that is not handled correctly
Alexander McLin (Feb 02 2023 at 21:47):That's what I thought, shall I open an issue about the last problem? Is the first problem already documented?
Folkert de Vries (Feb 02 2023 at 21:52):I don't think it is, but I haven't worked on the repl in a long time. @Richard Feldman you did some recent repl work right?
Folkert de Vries (Feb 02 2023 at 21:52):in any case: yes please open issues. We'll deal with any duplicates
Richard Feldman (Feb 02 2023 at 21:57):yeah those both look like bugs to me!
Matthias Toepp (Apr 18 2023 at 14:32):Here's a repl session from just now....What am I missing?
» x = 5
── MISSING FINAL EXPRESSION ────────────────────────────────────────────────────
I am partway through parsing a definition, but I got stuck here:
1│ app "app" provides [replOutput] to "./platform"
2│
3│ replOutput =
4│ x = 5
^
This definition is missing a final expression. A nested definition
must be followed by either another definition, or an expression
x = 4
y = 2
x + y
(That was the online repl)
Folkert de Vries (Apr 18 2023 at 14:38):I think you're missing indentation on tha tfinal line (line 4)?
Anton (Apr 18 2023 at 14:39):No, it also happens with indentation, did we not implement our assignment magic in the web repl?
Matthias Toepp (Apr 18 2023 at 14:42):@Folkert de Vries ...not sure what you mean by missing indentation...I'm only writing: "x = 5" into the repl.
Anton (Apr 18 2023 at 14:42):This looks like a bug in the web repl @Matthias Toepp, it does work on the local repl (roc repl using a nightly release)
Anton (Apr 18 2023 at 14:43):nightlies are available here btw
Anton (Apr 18 2023 at 14:45):@Brian Carroll is this a regression in the web repl or do we still have to implement automatic handling of assignments that do not return anything?
Matthias Toepp (Apr 18 2023 at 14:50):should i open an issue for this?
Matthias Toepp (Apr 18 2023 at 14:51):(thanks @Anton )
Anton (Apr 18 2023 at 14:52):should i open an issue for this?
yes please :)
Matthias Toepp (Apr 18 2023 at 14:52):ok...(i'm still impressed that there is an online repl! :)
Matthias Toepp (Apr 18 2023 at 14:59):opened issue: https://github.com/roc-lang/roc/issues/5301
Brendan Hansknecht (Apr 18 2023 at 15:46):I think the web repl has always been more picky about just doing assignment. It doesn't seem to keep state like the local repl. It needs every definition and the final expression all at once.
Brendan Hansknecht (Apr 18 2023 at 15:47):Maybe that is a regression. If so, it happened a while ago.
Brian Carroll (Apr 18 2023 at 20:24):It's not a regression or a bug, it was just never implemented
Brian Carroll (Apr 18 2023 at 20:55):The web repl and cli REPL have separate front ends, handle newlines differently, etc. The web repl currently only takes expressions, not definitions. The logic could be connected up but it hasn't been. Would be a great contribution if someone wants to do it!
David Dunn (Jun 03 2023 at 10:25):I've found panics in the REPL when there are type mismatches:
Str.joinWith ", " ["Hi", "World"] producesthread 'main' panicked at 'TODO turn fn_var into a RuntimeError Erroneous', crates/compiler/mono/src/ir.rs:4654:39
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Str.joinWith ["Hi", "World"] 42 producesthread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Erroneous', crates/compiler/mono/src/ir.rs:8875:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Found in the CLI REPL on ARM MacOS 13.4, using nightly 58067f9 (2023-06-02). Reproduced on the web REPL too. Couldn't find issues for these - should I open one?
Anton (Jun 03 2023 at 10:31):should I open one?
Go ahead :)
David Dunn (Jun 03 2023 at 10:34):There's also a panic in the CLI REPL when using undefined variables:
Str.joinWith [greeting, audience] ", "
"8\x9e\xf7\x05\x01"
thread 'main' panicked at 'Roc hit an error', crates/repl_cli/src/cli_gen.rs:133:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
This works as expected in the web REPL, printing the friendly UNRECOGNIZED NAME message.
Richard Feldman (Jun 03 2023 at 10:39):nice find, would love an issue for that one too! :smiley:
David Dunn (Jun 03 2023 at 10:45):Then there's a lesser issue where the web REPL inserts a newline before executing code when enter is pressed. This produces an error message when the code before the cursor isn't a valid line for the REPL, eg.
Str.joinWith ["greeting", "audience"] ", "<cursor> runs fine.
Str.joinWith ["greeting", "<cursor>audience"] ", " produces UNFINISHED LIST.
Str.joinWith ["greeting", "audience"] "<cursor>, " produces ENDLESS STRING.
Anton (Jun 03 2023 at 11:18):Feel free to create issues, we prefer some accidental duplicate issues over unfiled issues
David Dunn (Jun 03 2023 at 11:23):Done!
Last updated: Jul 26 2025 at 12:14 UTC