Parsing error on - sign or -- sign

[berry]

Hi Dillon,

I encountered the following error:

Could not parse file `src/DesignCards.elm` at position 700. Errors:
expected end of input

I finally (took me a while) tracked this down to the two following situations. The first:

type
    CardType
    -- comment
    = NoType
    | Ideate
    | Validate
    | Create
    | Facilitate

Elm compiles this code just fine. But, npx elm-typescript-interop reports the error stated above. If I remove the -- comment or move it a line lower no error occurs.

The second situation:

-(sqrt (sWidth ^ 2 + sWidth ^ 2))

This is also valid Elm code, but npx elm-typescript-interop reports the error stated above. If I substitute the - sign with -1 * then no error occurs.

I am using Elm 0.19 en elm-typescript-interop version 0.0.15.

Berry.

[dillonkearns]

Hello @berry, unfortunately there are some parsing bugs for the Elm AST libraries out there. You can reproduce the parsing error by pasting it into elm-typescript-interop's underlying parser: https://tunguski.github.io/elm-ast/example/.

Also, neither Bogdanp/elm-ast nor tunguski/elm-ast are planning on updating for Elm 0.19.

tunguski/elm-ast#33 (comment)
Bogdanp/elm-ast#96 (comment)

I think that the Elm community would really benefit from a new Elm AST package that has 0.19 support and doesn't have so many parsing errors. Unfortunately, I don't have the bandwidth to be the one that takes that task on. But I would really love it if someone would step up to the challenge!

I'll close this issue here since I can't help fix it unfortunately. But feel free to open an issue on https://github.com/tunguski/elm-ast and I'll gladly update it if it gets solved there. Thanks!

[berry]

Hi @dillonkearns,

No problem. I already wondered why Elm 0.18 was being installed ;-)

I am certainly no expert on AST libraries. But, in Elm-Slack I found this library mentioned: Elm syntax. It is an Elm parser in Elm. It is 0.19 compatible. I tested it on the code examples mentioned earlier in this issue and it parsed the code correctly. But, maybe you already know this library

I actually found some discussion in elm-syntax on the possibility of using elm-syntax for sharing constants between Typescript and Elm ;-) See: stil4m/elm-syntax#24. That issue references other issues on Elm AST.

I do hope that this issue on an up-to-date Elm AST gets resolved, because I do like your approach with elm-typescript-interop a lot!

[dillonkearns]

Hello @berry, thank you for that suggestion! I wasn't aware of that library, I'll explore that! I'll create a separate issue to track that exploration. Thank you! 🙏

[dillonkearns]

Here's the issue for reference @berry: #17

[davetapley]

@dillonkearns hi, I'm also here because expected end of input.

Once I found this issue and your link to https://tunguski.github.io/elm-ast/example/ I was able to refactor around the quirks of elm-ast pretty quickly, so thanks for sharing that. However, I did quite a lot of head banging before that. So: Until #17 (or some other fix) is in, would you consider a PR to just print out your advice:

unfortunately there are some parsing bugs for the Elm AST libraries out there. You can reproduce the parsing error by pasting it into elm-typescript-interop's underlying parser: https://tunguski.github.io/elm-ast/example/.

After:

elm-typescript-interop/src/TypeScript/Parser.elm

Line 238 in 0c0c7de

"Could not parse file `{0}` at position {1}. Errors:\n{2}"

❓

[dillonkearns]

Hello @dukedave, thanks for the comment! That is an excellent idea. I would love a PR for that. And thanks for asking first, I always like to start with a discussion. This sounds like an uncontroversial one that I am definitely for so I would welcome a PR 👍

By the way, I'm going to be experimenting with https://github.com/stil4m/elm-syntax once I have some free time. I'm hoping that this might have fewer parsing bugs. But regardless, having a better error message would be very useful!

[muelli]

unfortunately there are some parsing bugs for the Elm AST libraries out there

FWIW: The IntelliJ Elm plugin has a decent Elm parser.

[dillonkearns]

@muelli I think the Elm IntelliJ plugin's Elm parser is highly specialized for building up a format for IntelliJ to consume. And it's also in Kotlin. I'm hoping that still4m/elm-syntax will be up for the task!

[davetapley]

@dillonkearns I made that PR, BTW: #18

[MikeTschudi]

Here is another test case:

capitalize : String -> String
capitalize inValue =
    let
        tempValue = String.toUpper inValue  -- List E.Value
        outValue = String.trim tempValue
    in
        outValue

The trailing comment breaks the parser. A line after the line with the comment appears to be necessary for the break.

I am using Elm 0.19 and elm-typescript-interop version 0.0.15. Reproduced by inserting into elm-typescript-starter before update.