[ydj]

I think the facilities for building larger applications are lacking in APL. It would be great as something embedded into other languages. Consider something like numpy’s einsum, but using apl expressions instead. Use APL to express what it’s good at, and use the facilities of the host language to put together bigger systems.

[xelxebar]

Large parts of Sweden's health system run on APL; Deutsche Bank also uses lots of APL; Denkmark has an appreciable number of companies using APL. IMHO, the problem isn't the scalability of APL (Dyalog, specifically) but more that good, maintainable, solid APL violates what the industry holds up as Best Practices etc. Trying to apply typical software architecture methodologies to APL definitely evokes the feeling you describe.

However, APL in my experience enables radical simplicity for building large applications. Learning to leverage that means that you need to first unlearn lots of ingrained problem-solving habits and ways of thinking as a software engineer. It's admittedly a steep hill to climb.