Annex 1:

Functional programming concepts

with Java & VAVR

#EYD

v0.1.0

Functional Concepts

1. Eager vs Lazy
2. Mutable vs Immutable
3. Pure vs Impure functions
4. Side effects
5. List manipulation
6. Equational reasoning
7. Functional composition
8. Referential Transparency
9. Monads
10. Effects

Eager vs Lazy

Mutable vs Immutable

Pure vs Impure functions

Characteristics of Pure Function:

• The return value of the pure functions solely depends on its arguments Hence, if you call the pure functions with the same set of arguments, you will always get the same return values.
• They do not have any side effects like network or database calls
• They do not mod­ify the arguments which are passed to them

Side Effects

A side effect is any application state change that is observable outside the called function other than its return value.

Equational reasoning

Equational reasoning lets you transform consistently (based on mathematical functional equations) some functions into another ones

Functional composition

Functional composition

Function composition is a mechanism to combine simple functions to build more complicated ones.

The ability to easily compose functions encourages factoring (breaking apart) functions for maintainability and code reuse.

Referential Transparency

Referential transparency is generally defined as the fact that an expression, in a program, may be replaced by its value (or anything having the same value) without changing the result of the program.

Monads

A monad is just a monoid in the category of endofunctors.

A monad is a design pattern

A monad acts as a container that abstracts away those quirks in the computations, and let us focus more on what we want to do with the contained values.

Monads

Place a value into monadic context

• Haskell's Maybe: return / Just
• Scala's Option: Some
• Functional Java's Option: Option.some
• JDK8's Optional: Optional.of

Apply a function in monadic context

• Haskell's Maybe: >>= (aka bind)
• Scala's Option: flatMap
• Functional Java's Option: flatMap
• JDK8's Optional: flatMap

Effects

An effect is the thing a monad handles

• Optional is a monad that models the effect of optionality (of something being optional)
• CompletableFuture is a monad that models latency as an effect
• Try is a monad that models the effect of failures (manages exceptions as effects)
• Either is a monad that models the effect of failure and success