most values are not captured

[nickolay]

I'm new to Haskell and I don't know if or where I messed up, but none of the examples from the homepage work for me. Even something as simple as:

*Main Debug.Hood.Observe Lib> printO (observe "fun" . id $ 999)
999

-- fun
  _

For functions the output value is displayed, but the input parameters are displayed as _:

*Main Debug.Hood.Observe Lib> runO $ print $ observe "sum xs" (\ xs ys -> sum xs) [0..2] [0..]
3

-- sum xs
  { \ _ _  -> 3
  }

I'm using hood-0.3.1 and:

$ stack ghc -- --version
The Glorious Glasgow Haskell Compilation System, version 8.2.2

hood-0.3 works fine.

I tried using the GHCi debugger and it seems that the captured events (using 0.3.1) in the first testcase were:

events = [Debug.Hood.Observe.Event
            2 (Debug.Hood.Observe.Parent 1 0)
            (Debug.Hood.Observe.Cons 0 "999"),
          Debug.Hood.Observe.Event
            2 (Debug.Hood.Observe.Parent 1 0) Debug.Hood.Observe.Enter,
          Debug.Hood.Observe.Event
            1 (Debug.Hood.Observe.Parent 0 0)
            (Debug.Hood.Observe.Observe "fun")]

while in the version 0.3 that works, the event with Cons has the ID = 3. Given that eventsToCDS appears to use this ID as an index into the out_arr array, this duplicate event ID seems to be the problem.

Seems to be caused by the change to unsafeWithUniq in #6 -- moving incrementUniq node before the fn call fixes the problem for me.

[RyanGlScott]

Thoughts, @igrep?

[igrep]

I'm sorry for adding a big bug... I've scarcely used hood since the fix...
Anyway, I think @nickolay's fix would be OK if the test case I wrote passes (runs without error).

Thank you very much!

[nickolay]

FWIW, I didn't suggest "moving incrementUniq node before the fn call" as a proper fix, as I think it basically undoes the fix from #6: we would no longer "[increment] the node id only when the function is executed without exception". If one wanted to do that, he could revert the whole commit.

[mberkowitz]

I too am a novice and ra ninto the same bug -- the simple examples print data as _. Very disappointing.
A git rebase that omits all of pull request 6 seems to fix it.

As a beginner, I can't assess hood as a development tool, but it's intriguing and seems useful for learning haskell.
Why is it left in this broken state for 2.5 yrs? Why aren't the examples in the github repo, and what good is running CI when it can't detect this degree of failure?

[smith558]

The issue is still present in 2021. hood-0.3.1 not functional