In addition, I don't know how to implement this function correctly.
For example, if you alias ghc to another name the heuristic in the
executable-path package fails:

Good point. For the use case mentioned above, any quick and dirty heuristic that works most of the time would be sufficient, though.

Ideally, Haskell interpreters would set an environment variable when they interpret a source file.

Since

* we can't implement this reliably,

* the distinction into these three groups doesn't necessarily work for all compilers, and

* the distinction (I assume) isn't useful in most use cases

I think people who want to use this heuristic are better served by the existing executable-path package. What do you think?

-- Johan