Monads 101 with C++

Basics about functors and monads and implementation examples using modern C++

Transcript

1. Monads 101 with C++ Denis Kormalev Las Vegas, NV, 2018
2. Functors
3. ©Aditya Bhargava
4. Functor operations • Type constructor • unit • map (or fmap in Haskell )
5. Functor laws • Identity: • x.map(Identity) === x • Composition: • x.map(A).map(B) === x.map(AandB)
6. Monads
7. ©Aditya Bhargava
8. Monad operations • Type constructor • unit • flatMap (or bind in Haskell) • Monad is usually a functor
9. Monad laws • Left identity: • Monad.unit(x).flatMap(A) === A(x) • Right identity: • x.flatMap(Monad.unit) === x • Associativity: • x.flatMap(A).flatMap(B) === x.flatMap(xx -> A(xx).flatMap(B))
10. Option monad
13. Either monad Not really a monad, but we can alter it a bit to be one
18. List monad
22. Other useful monads • Eval • Delays calculation and trampolines its flatMaps • Future • Represents value that will be accessible at some future point of timeline • Reader • Carries value through morphisms (e.g. configuration) • Writer • Returns some additional data with the answer (e.g. logging) • State • Combination of Reader and Writer, carries data through morphisms and allows to change it
23. Referential transparency
24. Monad transformers
31. Other useful morphisms at OptionT • Option<T> -> Option<NewT> • Option<T> -> M<Option<NewT>> • M<?> -> NewM<?>
32. Questions?