Re: Difficulty integrating with Swift/Objective-C

[paul <paul@inktvis.org>]

Hello again list, Taylan,

On 2021-09-05 at 18:26 AEST, quoth Taylan Kammer 
<taylan.kammer@gmail.com>:
> To narrow down the issue, I'd attempt a few things, in order:
>
> 1. Compile only the C code, adding a main() function, just to 
> make sure the OS
>    and the chosen Guile version and such are working fine with 
>    each other.
>
> 2. Compile pure Objective-C code, calling that run_guile() 
> function firstly
>    directly from the main() function in main.m of the 
>    Objective-C program, and
>    commenting out the NSApplicationMain() call that would 
>    initialize Apple's
>    application framework.
>
> 3. See if reactivating the NSApplicationMain() call causes 
> problems.  (It should
>    be called *after* the Guile initialization.)
>
> 4. See if you can use Guile's C functions from 
> -applicationDidFinishLaunching:
>    e.g. by doing: scm_c_eval_string("(begin (display 
>    'HelloWorld) (newline))")
>
> If that works, we now have an Objective-C + Guile application, 
> and want to move
> to using Swift instead.  This is where my Apple knowledge hits 
> its limits because
> I never used Swift. :-)
>
> But I guess Swift should have something equivalent to the main() 
> function of C and
> Objective-C, and calling Guile initialization from there might 
> do the trick.

Thank you very much for your tips.  I was actually able to unstick 
myself with your suggestions: first i created a blank Objective-C 
CLI app and integrated Guile, that worked well!  Next i created a 
new, blank, Objective-C AppKit GUI app.  The same procedure worked 
well there, too.

The more challenging bit was learning how to take my existing 
Swift app and (re-)introduce a main() in Objective-C.  Because it 
turns out that Swift has some conveniences that cause it to 
autogenerate a _main symbol behind-the-scenes.  In any case you 
can turn that off and create an Objective-C main function (my 
project didn't have Objective-C to start with, but it was enough 
to create a new file with a main() copied from my earlier 
from-scratch experiments) which - long story short - i was able to 
modify and get Guile booting correctly!  I was even able to 
complete step 4, to my surprise (sort of), and call 
scm_c_eval_string straight from my Application Kit code.  This 
takes a bit of fiddling (Apple's so-called Precompiled Bridging 
Header) to make Swift aware of C-land functions, but my app 
actually already has a Rust-based core which i call out to with 
this mechanism so here i was on firmer ground.

I think there must have been something weird about the state of my 
project last night, because initially i was still having the 
EXC_BAD_ACCESS issues, but making a new branch off my main and 
doing the above worked well.

It should be said that i still couldn't use the Homebrew-packaged 
version of Guile because of the JIT errors i described elsewhere, 
but this isn't a blocker because i'm able to compile my own 
libguile with `--enable-jit=no`.

Thanks again, i spent all weekend messing with this and couldn't 
figure it out, your input was super useful.

All the best,
p.