> * we can't implement this reliably,
If I understand correctly the current System.Environment.getProgName can
make this distinction somehow. But from a quick peek at the code, I
can't really tell how it's done.
It doesn't. It returns whatever string follows the last / in argv[0]. argv[0] can in theory be anything, including "my hair is on fire." :) See the earlier posts in this thread.
I don't think it's possible to implement this correctly, except if we change how GHC runs scripts (i.e. by setting an environment variable, but if you do that you might as well just check for the environment variable if you want to know if you're running as a script.)
> * the distinction into these three groups doesn't necessarily work for all
> compilers, and
If a compiler does not support script/interactive, it could always
return Binary, right?
It might also have some 4th, non-compatible option. Even if it only haves a subset, it forces the programmer to write a pattern match that doesn't make sense (as some of the options can never happen.) getExecutablePath :: IO FilePath doesn't have this problem, as it's always defined.
> * the distinction (I assume) isn't useful in most use cases
At this point I would find it useful to define use cases. When I was
looking for that functionality, I wanted to find files relative to a
script. For binaries I use Cabal's support for data files, but this
only works for `cabal install`ed packages.
I guess my point is that we cannot implement what you want correctly. We can implement a heuristic that kind-of works most of the time. That's a useful thing to have, but if so as a function built upon a more well-defined getExecutablePath.
> I think people who want to use this heuristic are better served by the
> existing executable-path package. What do you think?
I still think that a well-tested, reliable way to do that would be
awesome. I'm not sure how hard it is to get it right, though.
If we do not support interactive/script, then I think we should at least
use a Maybe instead of `error`.
getExecutablePath :: IO FilePath
is always defined. It returns the path to the currently running executable, which is e.g. /bin/ghc in case of a script.
-- Johan