5 minute fp-ts fundamental overview

FP-TS__looking_around.ts

import assert from 'assert'

import * as Ma from 'fp-ts/Magma'
import * as Fu from 'fp-ts/Functor'
import * as Ap from 'fp-ts/Applicative'

import * as FN from 'fp-ts/function'

import * as B from 'fp-ts/boolean'
import * as S from 'fp-ts/string'
import * as N from 'fp-ts/number'
import * as A from 'fp-ts/Array'


/* ==================================================================

* boolean

** INSTANCES

B.BooleanAlgebra
B.Eq
B.MonoidAny
B.MonoidAll
B.Ord
B.SemigroupAny
B.SemigroupAll
B.Show

** REFINEMENTS

B.isBoolean

** PATTERN MATCHING

B.fold
B.foldW
B.match
B.matchW

*/

assert.strictEqual(
  B.MonoidAll.concat(true, false),
  false
)

assert.strictEqual(
  Ma.concatAll(B.SemigroupAll)(true)([true, true, true, true]),
  true
)

assert.strictEqual(
  FN.pipe(true, B.fold(FN.constant(1), FN.constant(2))),
  2
)

assert.strictEqual(
  FN.pipe(true, B.foldW(FN.constant(1), FN.constant('2'))),
  '2'
)

assert.strictEqual(
  FN.pipe(true, B.match(FN.constant(1), FN.constant(2))),
  2
)

assert.strictEqual(B.isBoolean("true"), false)

assert.strictEqual(B.isBoolean(false), true)


/* ==================================================================

* number

** INSTANCES

N.Bounded
N.Eq
N.Ord
N.Field
N.MagmaSub
N.SemigroupProduct
N.SemigroupSum
N.MonoidProduct
N.MonoidSum
N.Show

** REFINEMENTS

isNumber

*/

assert.strictEqual(N.isNumber(1), true)
assert.strictEqual(N.isNumber('1'), false)

assert.strictEqual(N.Bounded.bottom, -Infinity)
assert.strictEqual(N.Bounded.top, Infinity)

assert.strictEqual(N.Bounded.compare(1, 1), 0)
assert.strictEqual(N.Bounded.compare(1, 2), -1)
assert.strictEqual(N.Bounded.compare(2, 1), 1)

assert.strictEqual(N.Bounded.equals(N.Bounded.bottom, -Infinity), true)

assert.strictEqual(N.SemigroupProduct.concat(2, 3), 6)
assert.strictEqual(N.SemigroupSum.concat(2, 3), 5)

assert.strictEqual(N.MonoidProduct.empty, 1)
assert.strictEqual(N.MonoidSum.empty, 0)

assert.strictEqual(Ma.concatAll(N.MonoidProduct)(1)([1, 2, 3]), 6)
assert.strictEqual(Ma.concatAll(N.MonoidSum)(0)([1, 2, 3]), 6)

assert.strictEqual(
  FN.pipe([1, 2, 3, 4], Ma.concatAll(N.MonoidProduct)(1)),
  24
)


/* ==================================================================

* string

** INSTANCES

S.Eq
S.Ord
S.Monoid
S.Semigroup
S.Show

** REFINEMENTS

S.isString

** UTILS

S.empty
S.replace
S.size
S.slice
S.split
S.toLowerCase
S.toUpperCase
S.trim
S.trimLeft
S.trimRight
S.isEmpty
S.includes
S.startsWith
S.endsWith

*/

assert.strictEqual(FN.pipe('hello', S.isEmpty), false)
assert.deepEqual(FN.pipe('hello world', S.split(/\s+/)), ['hello', 'world'])


/* ==================================================================

* function

** INSTANCES

FN.getBooleanAlgebra
FN.getMonoid
FN.getSemigroup
FN.getSemiring
FN.getRing

let f = FN.getBooleanAlgebra(booleanAlgebraVoid)
console.log(f())

*/

let x = FN.getMonoid(N.MonoidSum)<string>()
let y = x.concat(x => x.length, y => y.length)('12345')
assert.strictEqual(y, 10)






/* ==================================================================

* Functor

*/

Fu.bindTo
Fu.flap
Fu.let
Fu.map

assert.deepEqual(
  A.Functor.map([1, 2, 3], x => x.toString().repeat(x)),
  ["1", "22", "333"]
)


/* ==================================================================

* Apply & Applicative

*/

Ap.getApplicativeMonoid

assert.deepEqual(
  A.Apply.ap([x => x + 1, x => x * 2], [1, 2, 3]),
  [2, 3, 4, 2, 4, 6]
)

assert.deepEqual(A.Applicative.of(0), [0])


// `map` vs `lift`
// Kita bisa membuat `lift` menggunakan `map` dan sebaliknya.

interface IFn1 { (x: number): number }
interface IFn2 { (x: number): IFn1 }
interface IFn3 { (x: number): IFn2 }
interface IFn4 { (x: number): IFn3 }

let lift = (f0: IFn1) => (xs: number[]) => A.Functor.map(xs, f0)

// Ternyata, A.map adalah lift

let f1: IFn1 = x => x + 1

assert.deepEqual(
  lift(f1)([1, 2, 3]),
  [2, 3, 4]
)

assert.deepEqual(
  lift(f1)([1, 2, 3]),
  A.map(f1)([1, 2, 3])
)

assert.deepEqual(
  FN.pipe(f1, lift, x => x([1, 2, 3])),
  FN.pipe([1, 2, 3], A.map(f1))
)


/* ==================================================================

* lifting -- An operation of Applicative

* lift   (a -> b)           :: F a -> F b
* liftA2 (a -> b -> c)      :: F a -> F b -> F c
* liftA3 (a -> b -> c -> d) :: F a -> F b -> F c -> F d

f1 :: a -> b
f2 :: a -> b -> c
f3 :: a -> b -> c -> d

pipe(of(f1), ap([1, 2]))
pipe(of(f2), ap([1, 2]), ap([10]))
pipe(of(f3), ap([1, 2]), ap([10]), ap([100]))

*/

// `liftA1`

assert.deepEqual(
  A.ap([1, 2, 3])(A.of(f1)),
  [2, 3, 4]
)

assert.deepEqual(
  FN.pipe([1, 2, 3], A.map(f1)),
  [2, 3, 4]
)

assert.deepEqual(
  FN.pipe(A.of(f1), A.ap([1, 2, 3])),
  [2, 3, 4]
)


// `liftA2`

let f2: IFn2 = x => y => x + y

assert.deepEqual(
  FN.pipe([1, 2, 3], A.map(f2), A.ap([10])),
  [11, 12, 13]
)

assert.deepEqual(
  FN.pipe(A.of(f2), A.ap([1, 2, 3]), A.ap([10])),
  [11, 12, 13]
)


// `liftA3` & `liftA4`

let f3: IFn3 = x => y => z => x + y + z

assert.deepEqual(
  FN.pipe(A.of(f3), A.ap([1, 2, 3]), A.ap([10]), A.ap([100])),
  [111, 112, 113]
)

let f4: IFn4 = x => y => z => a => x + y + z + a

assert.deepEqual(
  FN.pipe(A.of(f4), A.ap([1, 2, 3]), A.ap([10]), A.ap([100]), A.ap([1000])),
  [1111, 1112, 1113]
)