Starting Functional JavaScript

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Pure Functions

Functions that have no side effects are said to be pure.

Pure functions are useless, easily tested, and referentially transparent.

Currying

               and               

Partial Application

Curried Functions

Take their arguments one at a time.

Partial Application

Use closure to defer computation.

Partial application has many uses e.g. generic functions or fluent computations.

Function Composition

Use Case: Class Mixins

JavaScript class mixins are a way to share behaviour among classes

Pointfree Style

Functions which reference their own data are said to be "pointed". Likewise, functions which do not reference their parameters are said to be "pointfree". With curried and point-free functions, always take your data as the last parameter.

Functors

A functor is a container for some value, like an envelope. Functors can map from some value x in a category to another value y in that same category. Array and Promise are both functors.

Crocks Helpers

Crocks Logic

Crocks Curry

Crocks' curry is very flexible.

Monoids

A monoid is a type which has an 'empty' value, and an operation to combine values. Combining a value with the 'empty' value always produces the same value.

• What is the empty value for numbers under addition?
• Under multiplication?

You're already using monoids!

• && forms a monoid with true as empty value
• || forms a monoid with false as empty value
• String#concat forms a monoid with '' as empty value.
• Object.assign forms a monoid with {} as empty value
• Array#concat forms a monoid with [] as empty value

mreduceMap

Folds an array under a monoid of your choice, first mapping your monoid constructor over it.

Monad

Like a functor, Monads can map over their contents. Monads have the added ability to unwrap their self-similar contents. This power is called chain, bind, or flatMap

Maybe Monad

The Maybe monad wraps a value which may not exist. It has two instances: Just a and Nothing. Mapping over a Just works as expected. Mapping over a Nothing skips execution.

Maybe Monad - Binary

Maybe Monad - Binary

Thanks For

Watching!

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Benny Powers