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by ChadNauseam
1544 days ago
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It's surprisingly convenient when you get used to it. A very large proportion of values are only used once, so if a function only uses a value once you can mark it as being linear in that argument and get the relevant guarantees for very little mental overhead. You can still pass any value you want to the function, the only restriction is that the function must consume the value exactly once. It's tricky to write performant functional code, but personally I find linearity tagging a small price to pay for salvation (see this article I wrote, posted here: https://news.ycombinator.com/item?id=30762281 ). (Note that GHC currently doesn't use linearity for any performance optimizations, this is just a promising possible route.) One tidbit you might find interesting. Linear logic requires you use the value exactly once, but if you relax that requirement to "once or zero times" you get affine logic. (Values that don't have the any restriction on how much you can use them are called "exponentials".) With both linear and affine logic, you can pass an exponential to a function that's linear or affine in its argument – the only requirement is that the function uses the value in a linear or affine way. That's not quite the same as what Rust does, which I do find a bit annoying. What rust does is called "uniquenes typing", where a function can always do whatever it wants with any values it gets, but it can mark its parameters as "unique" and the caller has to make sure that any value passed as a parameter to that function is never used anywhere else. This is arguably the more useful of the two, because it means that you can mutate any argument marked as unique and no one can tell, but if you design a language around that you get Rust and I find Rust a bit less pleasant to program in than Haskell. |
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