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‎README.md‎

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@@ -141,7 +141,6 @@ Deeper understanding of Haskell performance, and how to improve it.
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## Worked examples
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* [Length-matched vectors](examples/length-matched-vectors.md)
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* [Validation Applicative](examples/validation-applicative.md)
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* [Rate limiting using STM](https://github.com/snoyberg/rate-limit)
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* [RWST in terms of IORef](https://gist.github.com/snoyberg/7ac111bc873be6a361e452adb5454cb9)
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‎async.md‎

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_very bad code_, don't do this!
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__Exercise__ Switch the import from `Control.Exception` to
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`Control.Exception.Safe`. What happens? Why?
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`UnliftIO.Exception`. What happens? Why?
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### Linking
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be aware of is that the `Async` data type will take an extra type
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paramter for the underlying monad.
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FIXME: copy material from
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* [async](https://haskell-lang.org/library/async)
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* __Exercise__: Write a concurrent program that prints the numbers 1 to 100 in
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one thread, pausing one second between number, and printing "Hello World"
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seconds in another thread
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## Section exercise
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Write a helper function which allows you to pass actions to worker

‎examples/length-matched-vectors.md‎

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# Length matched vectors
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FIXME
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```haskell
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{-# LANGUAGE NoImplicitPrelude #-}
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{-# LANGUAGE RankNTypes #-}
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{-# LANGUAGE ScopedTypeVariables #-}
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{-# LANGUAGE FlexibleContexts #-}
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module VectorLenMatched
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( VectorLM
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, LMKey
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, lmKeys
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, unVectorLM
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, lookupVectorLM
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, withVectorLM
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, newVectorLM
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, unknownKey
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) where
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import RIO
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import qualified RIO.Vector as V
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import RIO.Vector.Unsafe (unsafeIndex)
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import Data.Proxy
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import Data.Reflection
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import Data.Void
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newtype LMKey k = LMKey Int
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newtype VectorLM k a = VectorLM (Vector a)
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unknownKey :: Vector a -> VectorLM () a
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unknownKey = VectorLM
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unVectorLM :: VectorLM k a -> Vector a
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unVectorLM (VectorLM v) = v
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lookupVectorLM :: LMKey k -> VectorLM k a -> a
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lookupVectorLM (LMKey idx) (VectorLM v) = unsafeIndex v idx
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lmKeys :: forall k. Reifies k Int => [LMKey k]
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lmKeys =
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case reflect (Proxy :: Proxy k) of
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0 -> []
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i -> map LMKey [0..i - 1]
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withVectorLM
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:: forall a r.
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Vector a
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-> (forall k. Reifies k Int => VectorLM k a -> r)
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-> r
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withVectorLM v inner = reify (V.length v) $ \p -> inner $ addType p v
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addType :: proxy k -> Vector a -> VectorLM k a
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addType _ = VectorLM
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newVectorLM :: forall k a. Reifies k Int => Vector a -> Maybe (VectorLM k a)
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newVectorLM v
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| V.length v == len = Just (VectorLM v)
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| otherwise = Nothing
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where
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len = reflect (Proxy :: Proxy k)
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```

‎examples/validation-applicative.md‎

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