3 ms·

The 'IO wall' as you put it is the main thing I have not been able to wrap my head around. Most of the examples I have seen of FP-implementation-of-X leave this

The 'IO wall' as you put it is the main thing I have not been able to wrap my head around. Most of the examples I have seen of FP-implementation-of-X leave this bit out, or at best is a passing mention left as a 'reader exercise'. Most of us probably already follow best practices in terms of small functions, no global state, promises, composability etc. But at the end of every chain I have a db query and most of those mutate some data or other. Hopefully some day it clicks.

codygman 11y ago
> Hopefully some day it clicks. While you wait for that, try writing useful code despite not fully understanding it. Tell me what you think of the following code examples: > sum . take 2 $ [1,2,3,4,5] 3 > -- now lets pretend we have a list of numbers we got from the DB > let mockDBResponse = return [1,2,3,4,5] :: IO [Int] > -- first lets try the exact same code as above > sum . take 2 $ [1,2,3,4,5] 3 > sum . take 2 $ mockDBResponse <interactive>:46:16: Couldn't match expected type ‘[c]’ with actual type ‘IO [Int]’ Relevant bindings include it :: c (bound at <interactive>:46:1) In the second argument of ‘($)’, namely ‘mockDBResponse’ In the expression: sum . take 2 $ mockDBResponse > -- what to do? Use <$> > import Control.Applicative ((<$>)) > sum . take 2 <$> mockDBResponse 3 1) Applying pure functions to pure functions sum . take 2 $ [1,2,3,4,5] 2) Applying pure functions to monadic functions that implement fmap of the Functor typeclass sum . take 2 <$> [1,2,3,4,5] When I noticed that adding brackets around $ allowed me to apply pure functions to monadic ones a lot more made sense to me.
atrilumen 11y ago
Immutability is useful everywhere in the stack, even the database. See "Turning the database inside out with Apache Samza" by Martin Kleppmann: https://www.youtube.com/watch?v=fU9hR3kiOK0 https://www.youtube.com/watch?v=fU9hR3kiOK0

codygman 11y ago

> Hopefully some day it clicks. While you wait for that, try writing useful code despite not fully understanding it. Tell me what you think of the following code examples: > sum . take 2 $ [1,2,3,4,5] 3 > -- now lets pretend we have a list of numbers we got from the DB > let mockDBResponse = return [1,2,3,4,5] :: IO [Int] > -- first lets try the exact same code as above > sum . take 2 $ [1,2,3,4,5] 3 > sum . take 2 $ mockDBResponse <interactive>:46:16: Couldn't match expected type ‘[c]’ with actual type ‘IO [Int]’ Relevant bindings include it :: c (bound at <interactive>:46:1) In the second argument of ‘($)’, namely ‘mockDBResponse’ In the expression: sum . take 2 $ mockDBResponse > -- what to do? Use <$> > import Control.Applicative ((<$>)) > sum . take 2 <$> mockDBResponse 3 1) Applying pure functions to pure functions sum . take 2 $ [1,2,3,4,5] 2) Applying pure functions to monadic functions that implement fmap of the Functor typeclass sum . take 2 <$> [1,2,3,4,5] When I noticed that adding brackets around $ allowed me to apply pure functions to monadic ones a lot more made sense to me.

atrilumen 11y ago

Immutability is useful everywhere in the stack, even the database. See "Turning the database inside out with Apache Samza" by Martin Kleppmann: https://www.youtube.com/watch?v=fU9hR3kiOK0 https://www.youtube.com/watch?v=fU9hR3kiOK0