yogsototh/snoyman.com-content
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Some slide improvements

Browse source
This commit is contained in:
Michael Snoyman 2017-10-19 09:35:42 +03:00
parent d9b75a78fe
commit fadde0d137
No known key found for this signature in database
GPG key ID: A048E8C057E86876
1 changed files with 24 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

28
reveal/monad-transformer-state.md
View file

@ -37,7 +37,7 @@ title: Everything you didn't want to know about monad transformer state
*No trick question here*
* I have `foo :: IO a` and `bar :: IO b`. I want to run both at the same
I have `foo :: IO a` and `bar :: IO b`. I want to run both at the same
time in separate threads. How do I do that?
```haskell
@ -48,16 +48,35 @@ concurrently foo bar :: IO (a, b)
----
## An extra argument
Let's slightly modify things:
```haskell
foo :: MyEnv -> IO a
bar :: MyEnv -> IO b
baz :: MyEnv -> IO (a, b)
baz myEnv = concurrently (foo myEnv) (bar myEnv)
```
So far so good?
----
## What about ReaderT?
* Let's change the game a bit:
Explicit arguments are so boring! Let's move over to `ReaderT`.
```haskell
foo :: ReaderT MyEnv IO a
bar :: ReaderT MyEnv IO b
baz :: ReaderT MyEnv IO (a, b)
baz = concurrently foo bar -- bad!
```
* Now `concurrently` doesn't type match!
* Now `concurrently` doesn't type check!
* Can we make this work anyway?
----
@ -137,7 +156,8 @@ main = do
print res
```
What happened to 3?
* Outputs `4`
* What happened to `3`?
----