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Michael Snoyman 2017-10-26 16:09:39 +02:00
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19
reveal/monad-transformer-state.md
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@ -396,11 +396,22 @@ finallyS (StateT f) (StateT g) =
----
## What about bracket_?
## The problem cases
1. Could reimplement `bracket_` specifically for `StateT` to keep
state (exercise for the reader)
2. Could define a safe-for-`StateT` `bracket_`:
Two categories of problem cases
1. Things like `finally`: can manually reimplement them to get the
state retaining behavior desired. Problems:
* End up with mismatched semantics between libraries (the
`bracket_` example).
* Tedious and error-prone to reimplement these functions.
2. Things which _cannot_ be solved, like `concurrently`
----
## Cheating
Could define a safe-for-`StateT` `bracket_`:
```haskell
bracket_