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Better rows vs columns

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Michael Snoyman 2017-10-15 17:31:41 +03:00
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38
reveal/monad-transformer-state.md
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@ -20,7 +20,7 @@ title: Everything you didn't want to know about monad transformer state
* Example: `ReaderT` avoids needing to pass an extra argument to functions
* I'll explain transformer _environment_ and _state_ during the talk
---
----
## Which transformers are we covering?
@ -46,7 +46,7 @@ concurrently :: IO a -> IO b -> IO (a, b)
concurrently foo bar :: IO (a, b)
```
---
----
## What about ReaderT?
@ -60,7 +60,7 @@ bar :: ReaderT MyEnv IO b
* Now `concurrently` doesn't type match!
* Can we make this work anyway?
---
----
## Unwrap the `ReaderT`!
@ -79,7 +79,7 @@ concurrentlyR (ReaderT foo) (ReaderT bar) =
After all, `ReaderT` is just a convenient way to avoid argument
passing.
---
----
## Ask, lift, and run
@ -97,7 +97,7 @@ concurrentlyR foo bar = do
* _Leading question_ Surely there must be some general way to write
`concurrently`, right?
---
----
## lifted-async
@ -139,7 +139,7 @@ main = do
What happened to 3?
---
----
## Playing with bracket_
@ -163,7 +163,7 @@ Trick question! Depends on which `bracket_` you use
Ahhhhh!!!
---
----
## Implement concurrently for StateT
@ -181,7 +181,7 @@ concurrentlyS (StateT f) (StateT g) = StateT $ \s0 -> do
We generated two states, and have to discard one of them!
---
----
## Implement bracket_ for StateT
@ -198,7 +198,7 @@ bracket_S (StateT f) (StateT g) (StateT h) = StateT $ \s0 ->
`h` doesn't see the new state from `f`, and `g` doesn't see the new
state from either `f` or `h`!
---
----
## How about `ExceptT`?
@ -229,7 +229,7 @@ More discarding!
Next: let's define those classes
---
----
## Control functions
@ -254,7 +254,7 @@ atomicModifyIORef :: IORef a -> (a -> (a, b)) -> IO b
modifyMVar_ :: MVar a -> (a -> IO a) -> IO ()
```
---
----
## Monad transformer environment versus state
@ -270,7 +270,7 @@ newtype ExceptT e m a = ExceptT ( m (Either e a))
e a)` instead of `m a`)
* `StateT` has both (`s` as input, `m (a, s)` as output)
---
----
## Unlifting
@ -281,7 +281,7 @@ newtype ExceptT e m a = ExceptT ( m (Either e a))
* Transformers with monadic state may require discarding when
unlifting
---
----
## ReaderT-like things
@ -314,7 +314,7 @@ catchS (StateT f) onErr = StateT $ \s ->
f s `catch` (flip runStateT s . onErr)
```
---
----
## What about bracket_?
@ -349,7 +349,7 @@ class MonadIO m => MonadUnliftIO m where
* https://www.stackage.org/package/monad-unlift
* Control.Concurrent.Async.Lifted.Safe
---
----
## Providing StateT and ExceptT features
@ -362,7 +362,7 @@ recommendations:
Prepare torches and pitchforks for the next two slides
---
----
## Use mutable variables
@ -373,7 +373,7 @@ Prepare torches and pitchforks for the next two slides
* Recommendation: default to `TVar` unless you have a good reason to
do otherwise
---
----
## Use runtime exceptions
@ -395,7 +395,7 @@ Prepare torches and pitchforks for the next two slides
* You'll sometimes get stuck using less elegant things...
* But at least they work :)
---
----
## References
@ -406,7 +406,7 @@ This talk is based on a series of blog posts. Get even more gory details!
* https://www.fpcomplete.com/blog/2017/07/the-rio-monad
* https://www.fpcomplete.com/blog/2017/07/announcing-new-unliftio-library
---
----
## Questions?