Failed pattern match at Effect.Aff

[felixSchl]

The following code causes an uncaught exception to be thrown:

  bracket
    (do
      v <- AVar.empty
      v <$ do
        liftEffect $ launchAff_ do
          delay $ 1.0 # Milliseconds
          AVar.kill (error "boom") v
    )
    (\_ _ ->
      void $ attempt $ pure unit
    )
    \v ->
      forever $ AVar.take v

/home/felix/projects/aff-bug/output/Effect.Aff/index.js:76
        throw new Error("Failed pattern match at Effect.Aff line 385, column 12 - line 387, column 20: " + [ v.constructor.name ]);
                                                                                                               ^

TypeError: Cannot read property 'constructor' of null
    at Object.isLeft (/home/felix/projects/aff-bug/output/Effect.Aff/index.js:76:112)
    at run (/home/felix/projects/aff-bug/output/Effect.Aff/foreign.js:508:27)
    at /home/felix/projects/aff-bug/output/Effect.Aff/foreign.js:333:19
    at drain (/home/felix/projects/aff-bug/output/Effect.Aff/foreign.js:120:9)
    at Object.enqueue (/home/felix/projects/aff-bug/output/Effect.Aff/foreign.js:141:11)
    at Timeout._onTimeout (/home/felix/projects/aff-bug/output/Effect.Aff/foreign.js:330:27)
    at ontimeout (timers.js:466:11)
    at tryOnTimeout (timers.js:304:5)
    at Timer.listOnTimeout (timers.js:267:5)

The error goes away in one of two conditions:

• don't AVar.take in the run handler
• don't use attempt

[natefaubion]

I think the minimal repro is:

  bracket
    (pure unit)
    (\_ → void $ try $ pure unit)
    (\_ → do
      delay (Milliseconds 1.0)
      throwError (error "Nope."))

Which gives me a bad exception. Removing the try results in the correct "Nope." exception. I suspect it has something to do with catch in a bracket cleanup.

There's nothing special about AVar actions (they are just normal async Aff bindings), so you can repro anything involving them by just replacing them with async resolution.

[natefaubion]

Minimal with primitives

  bracket
    (pure unit)
    (\_ → catchError (pure unit) (const (pure unit)))
    (\_ → throwError (error "Nope."))