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Simplified some text. Added link to FL.
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readme.md
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readme.md
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# Functional Programming Jargon
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> The whole idea of this repos is to try and define jargon from combinatorics and category theory jargon that are used in functional programming in a easier fashion.
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The goal of this document is to define jargon from functional programming in plain english with examples.
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*Let's try and define these with examples, this is a WIP—please feel free to send PR ;)*
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*This is a WIP—please feel free to send a PR ;)*
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> Where applicable, this document uses terms defined in the [Fantasy Land spec](https://github.com/fantasyland/fantasy-land)
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## Arity
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@ -77,7 +78,7 @@ curriedSum(40)(2) // 42.
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> A function which combines two values of a given type (usually also some kind of functions) into a third value of the same type.
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The most straightforward type of composition is called "normal function composition".
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The most well-known type of composition is normal function composition.
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It allows you to combines functions that accept and return a single value.
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```js
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@ -91,8 +92,8 @@ floorAndToString(121.212121) // "121"
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## Purity
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> A function is said to be pure if the return value is only determined by its
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input values, without any side effects.
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> A function is pure if the return value is only determined by its
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input values, and does not produce side effects.
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```js
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let greet = "yo";
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@ -123,15 +124,16 @@ console.log("IO is a side effect!");
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```
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---
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## Idempotency
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## Idempotent
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> A function is said to be idempotent if it has no side-effects on multiple
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executions with the the same input parameters.
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> A function is idempotent if reapplying it to its result does not produce a different result.
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`f(f(x)) = f(x)`
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`Math.abs(Math.abs(10))`
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`sort(sort(sort([2,1])))`
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---
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## Point-Free Style
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@ -172,27 +174,28 @@ Points-free function definitions look just like normal assignments without `func
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---
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## Value
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## Value
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> Any complex or primitive value that is used in the computation, including functions. Values in functional programming are assumed to be immutable.
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> Anything that can be assigned to a variable.
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```js
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5
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Object.freeze({name: 'John', age: 30}) // The `freeze` function enforces immutability.
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(a) => a
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[1]
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undefined
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```
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Note that value-containing structures such as [Functor](#functor), [Monad](#monad) etc. are themselves values. This means, among other things, that they can be nested within each other.
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---
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## Constant
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## Constant
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> An immutable reference to a value. Unlike variables in most languages, constants cannot be reassigned to a new value once defined.
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> An immutable reference to a value. Not to be confused with `Variable` - a reference to a value which can at any point be updated to point to a different value.
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```js
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const five = 5
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const john = {name: 'John', age: 30}
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```
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Constants are referentially transparent. That is, they can be replaced with the values that they represent without affecting the result.
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Constants are [referentially transparent](#referential-transparency). That is, they can be replaced with the values that they represent without affecting the result.
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In other words with the above two constants the expression:
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```js
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@ -205,9 +208,9 @@ Should always return `true`.
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## Functor
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> An object with a `map` function that adhere to certains rules. `Map` runs a function on values in an object and returns a new object.
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> An object with a `map` function that adheres to certain rules. `Map` runs a function on values in an object and returns a new object.
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Simplest functor in javascript is an `Array`
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A common functor in javascript is `Array`
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```js
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[2,3,4].map( n => n * 2 ); // [4,6,8]
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@ -216,16 +219,18 @@ Simplest functor in javascript is an `Array`
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Let `func` be an object implementing a `map` function, and `f`, `g` be arbitrary functions, then `func` is said to be a functor if the map function adheres to the following rules:
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```js
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// identity
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func.map(x => x) == func
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```
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and
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```js
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// composition
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func.map(x => f(g(x))) == func.map(g).map(f)
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```
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We can now see that `Array` is a functor because it adheres to the functor rules!
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We can now see that `Array` is a functor because it adheres to the functor rules.
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```js
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[1, 2, 3].map(x => x); // = [1, 2, 3]
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```
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@ -241,12 +246,12 @@ let g = x => x * 2;
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---
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## Pointed Functor
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> A functor with an `of` method. `Of` puts _any_ single value into a functor.
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> A functor with an `of` function that puts _any_ single value into that functor.
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Array Implementation:
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Array Implementation:
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```js
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Array.prototype.of = (v) => [v];
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[].of(1) // [1]
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```
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@ -342,7 +347,14 @@ The identity value is empty array `[]`
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```js
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[1, 2].concat([]); // [1, 2]
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```
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Functions also form a monoid with the normal functional compositon as an operation and the function which returns its input `(a) => a`
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If identity and compose functions are provided, functions themselves form a monoid:
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```js
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var identity = a => a;
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var compose = (f, g) => x => f(g(x));
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compose(foo, identity) ≍ compose(identity, foo) ≍ foo
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```
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---
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@ -358,7 +370,8 @@ Functions also form a monoid with the normal functional compositon as an operati
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['cat,dog','fish,bird'].map(a => a.split(',')) // [['cat','dog'], ['fish','bird']]
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```
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You may also see `of` and `chain` referred to as `return` and `bind` (not be confused with the JS keyword/function...) in languages which provide Monad-like constructs as part of their standard library (e.g. Haskell, F#), on [Wikipedia](https://en.wikipedia.org/wiki/Monad_%28functional_programming%29) and in other literature. It's also important to note that `return` and `bind` are not part of the [Fantasy Land spec](https://github.com/fantasyland/fantasy-land) and are mentioned here only for the sake of people interested in learning more about Monads.
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`of` is also known as `return` in other functional languages.
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`chain` is also known as `flatmap` and `bind` in other languages.
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---
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@ -403,7 +416,7 @@ CoIdentity(1).extend(co => co.extract() + 1) // CoIdentity(2)
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## Isomorphism
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> A pair of transformations between 2 types of objects that is structural in nature and no data is lost.
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> A pair of transformations between 2 types of objects that is structural in nature and no data is lost.
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For example, 2D coordinates could be stored as an array `[2,3]` or object `{x: 2, y: 3}`.
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```js
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