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I'm using WSL 2 Ubuntu 20.04 inside Windows 10. I have installed SoPlex, OSI, and Fast-Downward with LP support. I have tested my downward installation by finding some simple PDDL task and then running
./fast-downward.py problem.pddl task.pddl --search "astar(lmcut())"
The solver found a solution. So there isn't an issue with my downward installation.

I installed fast-downward (this repo Haskell interface) using cabal:
cabal install fast-downward
It installed version 0.2.1.0 (latest).

Then, I downloaded the Gripper.hs example from this repo, and deleted the line:
module FastDownward.Examples.Gripper where
I saved it, and compiled it with:
ghc -o Gripper Gripper.hs
It compiled successfully, so I ran it:
./Gripper

The only output is the error message:
Gripper: downward: createProcess: runInteractiveProcess: exec: inappropriate type (Not a directory)

It may be my Haskell inexperience, but if I want to run example.hs as code outside the package, bjolp can't be used (not exported): https://github.com/circuithub/fast-downward/blob/master/FastDownward/Examples/Gripper.hs#L84

It's unclear then how to create a solver: you can't create a "bjolp of your own" either since there are other instances not exported, and needed to create it.

The previous minor version example works fine though, so this is not stopping me from playing with the library, but you may want to check if it's really a problem or is just me.

Thanks!

When I run FastDownward/Examples/Gripper.hs, I get Couldn't find a plan! which is unexpected to me since in https://blog.ocharles.org.uk/posts/2018-12-25-fast-downward.html a plan is found. downward is on my PATH.

Using WSL2 on Windows 11.

Steps:

1. $ mkdir proj
2. $ cd proj
3. $ cabal init -p proj
4. Add fast-doward in proj.cabal:
   build-depends: base ^>=4.12.0.0, fast-downward >= 0.2.2.0
5. Replace app/Main.hs with the content of FastDownward/Examples/Gripper.hs from this repo, replacing the module line with module Main where
6. $ cabal run

Edit: Printing the result told me that there seems to be input error: Couldn't find a plan!InputError

Assuming that solving the example problem should give a plan, how would I go about debugging this issue?