Day 11: Plutonian Pebbles
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FAQ
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2 points
Does the IORef go upwards the recursion tree? If you modify the IORef at some depth of 15, does the calling function also receive the update, is there also a Non-IO-Ref?
2 points
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The IORef is like a mutable box you can stick things in, so readIORef returns whatever was last put in it (in this case using modifyIORef'). “last” makes sense here because operations are sequenced thanks to the IO monad, so yes: values get carried back up the tree to the caller. There’s also STRef for the ST monad, or I could have used the State monad which (kind of) encapsulates a single ref.
