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Comment by gautamcgoel | Hacker News Reader

Can someone explain what this means, practically speaking? I know Haskell fairly well, but am not familiar with linear types. These are types that can be used only once, right?

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They must be used once and exactly once, no more or less.

I liked this paper:

http://www.cs.utexas.edu/~hunt/research/hash-cons/hash-cons-...

And previous discussion: https://news.ycombinator.com/item?id=20369522

My understanding is that the current implementation is only groundwork for possible future performance benefits, since there are no changes to the runtime system or garbage collector, and that their current intended use is mostly for allowing library authors to encode safe session/resource handling in the type system. So, new libraries can make it a type error to fail to properly close a connection or release a shared resource.

Simon Peyton Jones talk: https://www.youtube.com/watch?v=t0mhvd3-60Y

You can write safe memory management libraries in userspace with the existing extension. That can help reduce GC pressure by moving data off-heap and allow for safer & more efficient FFI bindings.

As someone who has been exploring doing gamedev in Haskell, that all is very exciting and the use-cases are constantly obvious to me.

It is entirely up to userspace to leverage this new feature. It doesn't do anything on its own outside of the type-checker. And to use it, your library will probably have to do some unsafe coercion under the hood (just like ST uses unsafePerformIO under the hood to do pure mutability.)

Right, my understanding is that in a sense it doesn't "enable new performance", because operationally speaking it's all stuff you could do anyway. What it does is move a lot of potential approaches from "absurdly unsafe" to "perfectly fine", so whatever your threshold for safety it's likely to move some speed improvements over the line if you care much about speed.

Yes, it's useful for reasoning about resources (file handles, sockets, memory buffers) etc.

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