Recover in Elm

import Html exposing (text)

mayPanic : () -> a
mayPanic _ =
    Debug.todo "a problem"

main =
    let
        result =
            Result.fromMaybe "Recovered. Error:\n a problem" (mayPanic () |> Just)
    in
    case result of
        Ok _ ->
            text "After mayPanic()"
        
        Err message ->
            text message

In Elm, there isn’t a direct equivalent to Go’s panic and recover mechanisms. Elm is designed to handle errors in a more structured way, typically using the Result type. Here’s how we can adapt the concepts:

1. We define a mayPanic function that uses Debug.todo. This is somewhat analogous to a panic in Go, as it will cause a runtime error when executed.

2. Instead of using a deferred function with recover, we use Elm’s Result type to handle the potential error.

3. We wrap the call to mayPanic in a Result, using Result.fromMaybe. If mayPanic succeeds (which it won’t in this case), it would return Ok. When it fails, we get an Err with our error message.

4. In the main function, we pattern match on the Result. If it’s Ok, we would print “After mayPanic()” (which won’t happen in this case). If it’s Err, we display the error message.

To run this Elm program:

1. Save the code in a file named Recover.elm.
2. Use the Elm reactor or compile it to HTML:

$ elm reactor
# or
$ elm make Recover.elm

3. Open the resulting HTML file in a browser or navigate to the appropriate localhost address if using elm reactor.

The output will be:

Recovered. Error:
 a problem

This example demonstrates how Elm’s type system and Result type can be used to handle and recover from errors in a way that’s somewhat analogous to Go’s panic and recover, but in a more structured and type-safe manner.