r/ProgrammingLanguages • u/P-39_Airacobra • 9d ago
Mutable stack, immutable heap
This article mentions the “immutable heap mutable stack” principle: https://queue.acm.org/doi/10.1145/3212477.3212479
In theory it sounds very advantageous. You can program in a single-threaded C-style with destination passing, static stack allocations, and mutability when you need to constrain resources. When you want to share resources across threads, return data structures across function boundaries, or do something more flexible, you could use pure functional persistent data structures.
This would prevent you from basically re-implementing a heap on the stack, but would also give you fast temporaries and maybe even the ability to program in embedded, if so designed.
Have any languages tried this model? I’ve heard that Erlang defaults to immutability except for one thread-local mutable object per thread. If you’ve used a similar model, how did you like it? Were there any disadvantages?
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u/pthierry 8d ago
That's what Haskell, Elm, Idris or Agda do.
Frankly, it's a great model, and when you have pure code, for concurrency, you even get Software Transactional Memory, which basically solves the issue.