bug: "Exception: user error (unknown GLUT entry glutInit)" under ghci, but not when compiled (Linux)

[Eugene Crosser]

I've sent it to the bug reporting channel (email) specified in the package, but there was now reaction and it did not appear in trak. On github, bug tracker is disabled. So I am copying the report here:

=====

Linux Ubuntu eoan,
ghc 4.8.8, libghc-gloss-dev 1.13.0.1-2build1, freeglut3 2.8.1-3

Running example from the package description:


```
$ cat g.hs
import Graphics.Gloss
main = display (InWindow "Nice Window" (200, 200) (10, 10)) white (Circle 80)
```

When compiled, works as expected:

```
$ ghc --make g.hs && ./g
```

shows the window with the circle. However, when run under ghci it does not work:


```
$ ghci g.hs
GHCi, version 8.4.4: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( g.hs, interpreted )
Ok, one module loaded.
*Main> :main
*** Exception: user error (unknown GLUT entry glutInit)
*Main>
```

It is quite unfortunate to not be able to debug the code under ghci.

Thanks,

Eugene

[Ben Lippmeier]

Try starting ghci with -fasm and -fno-ghci-sandbox. Using Gloss + GLUT under ghci has never been completely stable. It tends to work on some platforms but not others. You could also try to use the GLFW wrapper using the instructions on http://gloss.ouroborus.net/

Ben.

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[Eugene Crosser]

It's been a long time!

But today I was frustrated by this problem again, and tried something that seems obvious in retrospect, i.e. use LD_PRELOAD to load libglut when starting ghci. And it worked!  So, there is a workaround for this problem. In my case (Ubuntu groovy), the command looks like this:

    LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libglut.so.3 ghci ...

After that, it is possible to run (`:main ...`) the application from ghci. Hope that this may help somebody.