Functional Programming Patterns

A short enumeration of selected patters occuring in FP.

Transcript

1. Functional Programming Patterns
2. 1st class functions Functions are values too. They have type. Can be assigned to variables. f: a b → g: (a, b) c → input type output type → multiple arguments
3. Higher order funs A higher order function is a function that takes other functions as argument. h: ([a], a b) [b] → → list elem mapper Strategy pattern-like
4. Currying f: (a, b) c → f: a b c → → f: a (b c) → → curried form right-associative Factory pattern-like
5. Pure Functions Referential transparency – expression replaceable with its value without changing program semantics. easy to reason about optimizable
6. Immutability Values are constructed and then never modified. persistent collections
7. tuples and Lists pair: (a, b) 3-tuple: (a, b, c) 1 :: 2 :: 3 :: Nil [1, [2, [3, []]]] heterogeneous fixed lengthc homogeneous unbounded length
8. Transform Recursion is low-level flow control. Usages can be abstracted. Tell what, not how. map, filter, fold
9. Algebraic Data Types data List a = Cons a (List a) | Nil data Tree a = Node (Tree a) a (Tree a) | Empty
10. Functor A functor is a computational context. Map applies a normal function to a value in a context. map: f a (a b) f b → → → F<A> (A B) F<B> → → → fmap
11. Monad point: a f a → flatMap: f a (a f b) f → → → b A context with richer operations. pure, return bind
12. Option Nulls made explicit. No more NPE. data Option a = Some a | None orElse: Opt a Opt a Opt a → → getOrElse: Opt a a a → → Monad
13. Either data Either a b = Left a | Right b Often used for error handling, where error is on the left, success on the right. Monad for a fixed a
14. Future Promise / Future is a context, where the contained computation may execute concurrently. Used to compose async computations without blocking. Monad
15. Typeclasses A typeclass describes a contract. A typeclass instance describes how a given data type fulfills that contract. Like an Adapter, but more versatile.
16. Semigroup Monoid , Semigroup defines addition. Monoid is semigroup with an identity element. Pops all over your code!
17. Foldable A foldable provides means for stateful traversal. foldLeft: f a b (b a b) b → → → → → Nice cooperation with Monoids
18. Extra stuff Applicative functors, Monad transformers, Relational databases, Linear logic, IO, DI, Logging, Total FP, Actors, ...
19. Thx