Using sandwich with IO and MonadError

[flip111]

Thanks for the cool library.

I have this piece of code, i can't really make much sense of the type errors. I'm not sure where to start to figure this out. Is it my code that is a problem or am i using sandwhich library code in the wrong way? I'm surprised by the first error about expectationFailure i thought i could use that like this directly.

Any pointers to get this to work would be appreciated

type MonadPipe m = (HasCallStack, MonadIO m, MonadError Error m)

B.connect :: MonadPipe m => HasCallStack => ValidatedConfig -> m Pipe

connect :: TopSpec
connect = do
  describe "Connect" $ do
    let config :: B.Config = def
    case B.validateConfig config of
      V.Failure err -> expectationFailure $ show err -- Line 31
      V.Success vconf -> do
        it "connects" $ do
          pipe <- B.connect vconf -- Line 34
          pure ()

errors

Main.hs:31:24: error:
    • Could not deduce (exceptions-0.10.4:Control.Monad.Catch.MonadThrow
                          (free-5.1.10:Control.Monad.Free.Free
                             (sandwich-0.1.2.0:Test.Sandwich.Types.Spec.SpecCommand
                                context IO)))
        arising from a use of ‘expectationFailure’
      from the context: HasBaseContext context
        bound by the type signature for:
                   connect :: TopSpec
        at test/Main.hs:26:1-18
    • In the first argument of ‘($)’, namely ‘expectationFailure’
      In the expression: expectationFailure $ show err
      In a case alternative:
          V.Failure err -> expectationFailure $ show err
   |       
31 |       V.Failure err -> expectationFailure $ show err
   |                        ^^^^^^^^^^^^^^^^^^
           
Main.hs:34:19: error:
    • Could not deduce (Control.Monad.Error.Class.MonadError
                          Database.Bolt.Connection.Type.Error (ExampleT context IO))
        arising from a use of ‘B.connect’
      from the context: HasBaseContext context
        bound by the type signature for:
                   connect :: TopSpec
        at test/Main.hs:26:1-18
    • In a stmt of a 'do' block: pipe <- B.connect vconf
      In the second argument of ‘($)’, namely
        ‘do pipe <- B.connect vconf
            pure ()’
      In a stmt of a 'do' block:
        it "connects"
          $ do pipe <- B.connect vconf
               pure ()
   |       
34 |           pipe <- B.connect vconf
   |    

[thomasjm]

The first error is because you're calling expectationFailure outside of an ExampleT. In general all the actual effectful test code should be wrapped in it blocks--if you move the it line to just after the describe line then it should work.

For the second error, I'm not sure what MonadPipe is but it's possible we don't have suitable instances yet for ExampleT. It's possible we could add a MonadError instance if that's all it needs. Are you trying to use this? It seems all that needs is MonadIO.