EEK-Whales

A collection of JavaScript/TypeScript modules for functional programming

API

Combinators

• identity :: a -> a
• constant :: a -> b -> a

Point-free Functions

• equals :: Setoid a => a -> a-> Boolean or a -> b -> Boolean

Classify Functions

• getType :: a -> String
• is :: String -> a -> Boolean

Predicate Functions

• isEqual :: a -> b -> Boolean
• isSame :: a -> b -> Boolean
• isSameType :: a -> b -> Boolean
• isTruthy :: a -> Boolean
• isNil :: a -> Boolean
• isFunction :: a -> Boolean
• isDate :: a -> Boolean
• isIterable :: a -> Boolean
• isSetoid :: a -> Boolean

Showable

• inspect :: a -> String
• nodeInspect :: Symbol

Number

• random :: (Number | Undefined) -> Number

Combinators

identity

identity :: a -> a
I :: a -> a

This is the identity (I) combinator. It takes a value and returns the same value.

import { identity, I } from "eek-whales"

identity(42) // => 42
identity("tacocat") // => "tacocat"
I(42) // => 42

constant

constant :: a -> b -> a

This is the K (Kestrel) combinator. It takes two values and returns the first.

import { constant } from "eek-whales"

constant(42)(73) // => 42
constant("Kestrel")("Identity") // => "Kestrel"

Point-free Functions

equals

equals :: Setoid a => a -> a -> Boolean
equals :: a -> b -> Boolean

The equals function is useful for deep equality comparisons or for comparing two values of the Setoid type. Returns true given two values that are deeply equal and false otherwise. Primitive values are checked using the isSame module. Setoids are compared using their equals or fantasy-land/equals methods.

import { equals } from "eek-whales"

equals ([1, 2, 3]) ([1, 2, 3])            // => true
equals ({ a: 1, b: 2 }) ({ a: 1, b: 2 })  // => true
equals (NaN) (NaN)                        // => true
equals ([]) ([])                          // => true

equals (0) (-0)                           // => false
equals ([4]) ([2])                        // => false

// `Max` is a Setoid [Object] with an `equals` method
equals (Max(42)) (Max(43))                // => false

Classify Functions

getType

getType :: a -> String

getType is a function that returns a value's type, given any value. The original version of this function was named type, but was changed to avoid conflicts with the TypeScript keyword.

import { getType } from "eek-whales"

getType("hello")            // => "String"
getType([1, 2, 3])          // => "Array"
getType(42)                 // => "Number"
getType(/^foo$/i)           // => "RegExp"
getType(<T>(x: T): T => x)  // => "Function"

// An object with a custom type
const MyCustomType = {
  "@@type": "CustomType",
}

// An object with a custom type using the Symbol.toStringTag
const AnotherCustomType = {
  get [Symbol.toStringTag]() { return "CustomType" },
}

getType(MyCustomType)       // => "CustomType"
getType(AnotherCustomType)  // => "CustomType"

is

is :: String -> a -> Boolean

The is function accepts two parameters. The first is a string that represents the type for the second parameter to be validated against. Uses getType on the second parameter for the comparison.

import { is } from "eek-whales"

is ("String") ("hello")   // => true
is ("String") (42)        // => false
is ("Array") ([1, 2, 3])  // => true
is ("Array") ({ a: 1 })   // => false
is ("Undefined") ()       // => true

is ("Max") (Max(42).concat(Max(41)))  // => true

Predicate Functions

isEqual

isEqual :: a -> b -> Boolean

The isEqual predicate function compares two values using the strict equality (===) comparison operator with the exception of NaN which returns true when compared with NaN.

import { isEqual } from "eek-whales"

isEqual("pizza")("pizza") // => true
isEqual(42)(42)           // => true
isEqual(NaN)(NaN)         // => true
isEqual({})({})           // => false
isEqual([6])([6])         // => false
isEqual("night")("day")   // => false

isSame

isSame :: a -> b -> Boolean

The isSame predicate function is similar to isEqual with the exception of negative zero (-0) and zero (0, +0) not being equal. It is equivalent to the JavaScript Object.is static method.

import { isSame } from "eek-whales"

isSame (0) (0)    // => true
isSame (0) (+0)   // => true
isSame (0) (-0)   // => false
isSame (-0) (+0)  // => false

isSameType

isSameType :: a -> b -> Boolean

isSameType accepts any value for both parameters and returns a boolean that represents if both parameters are of the same type.

import { isSameType } from "eek-whales"

isSameType ("hello") ("world")  // => true
isSameType (21) (42)            // => true
isSameType (null) (undefined)   // => false
isSameType ({}) ([])            // => false

isTruthy

isTruthy :: a -> Boolean

isTruthy returns the result of converting the given parameter into a boolean.

import { isTruthy } from "eek-whales"

isTruthy(true)        // => true
isTruthy({})          // => true
isTruthy([])          // => true
isTruthy(42)          // => true
isTruthy("0")         // => true
isTruthy(new Date())  // => true
isTruthy(Infinity)    // => true
isTruthy(false)       // => false
isTruthy(0)           // => false
isTruthy(-0)          // => false
isTruthy(0n)          // => false
isTruthy("")          // => false
isTruthy(null)        // => false
isTruthy(undefined)   // => false
isTruthy(NaN)         // => false

isNil

isNil :: a -> Boolean

isNil returns true given one of null, undefined, or NaN. All other values return false.

import { isNil } from "eek-whales"

isNil(null)       // => true
isNil(undefined)  // => true
isNil(NaN)        // => true
isNil("")         // => false
isNil(0)          // => false
isNil(42)         // => false
isNil([])         // => false

isFunction

isFunction :: a -> Boolean

isFunction returns true given a function or generator function. All other values return false.

import { isFunction } from "eek-whales"

const generator = function*() { yield "a"}
const fn = <T>(x: T): T => x

isFunction(fn)                         // => true
isFunction(<T>(x: T): T => x)          // => true
isFunction(generator)                  // => true
isFunction(function*() { yield "a" })  // => true
isFunction([])                         // => false

isDate

isDate :: a -> Boolean

isDate returns true given a date object. All other values return false.

import { isDate } from "eek-whales"

isDate(new Date())            // => true
isDate(new Date(2023, 1, 1))  // => true
isDate(Date.now())            // => false
isDate()                      // => false
isDate("Wed Feb 01 2023 00:00:00 GMT-0500 (Eastern Standard Time)") // => false

isIterable

isIterable :: a -> Boolean

isIterable returns true given a value with a Symbol.iterator static method.

import { isIterable } from "eek-whales"

isIterable("hello world")                               // => true
isIterable([1, 2, 3])                                   // => true
isIterable(new Uint8Array([10, 20, 30, 40, 50]))        // => true
isIterable(new Map([["a", 1], ["b", 10], ["c", 100]]))  // => true
isIterable(new Set([0, 1, 1, 2, 3, 5, 8, 13, 21, 34]))  // => true
isIterable(42)                                          // => false
isIterable({})                                          // => false
isIterable()                                            // => false

const customIterable = {
  *[Symbol.iterator]() {
    yield 1
    yield 2
    yield 3
  }
}

isIterable(customIterable)  // => true

isSetoid

isSetoid :: a -> Boolean

isSetoid returns true given an object/class with an equals or fantasy-land/equals method. All other values return false. This module relies on duck typing to check if a value is a Setoid. It does NOT validate any of the required algebraic laws (reflexivity, symmetry, and transitivity) as laid out in the Fantasy Land Specification. Validating the laws is not possible without knowing the type of value that will be passed to the equals method in advance and that will vary depending on the Setoid implementation.

import { isSetoid } from "eek-whales"
import { Min, Max } from "eek-whales"

isSetoid(Min)            // => true
isSetoid(Max)            // => true
isSetoid("hello world")  // => false

interface NumericSetoid {
  value: number
  equals: (n: NumericSetoid) => boolean
}

const mySetoid = (x: number) => ({
  value: x,
  equals: (y: NumericSetoid) => x === y.value
})

isSetoid(mySetoid(42))  // => true
isSetoid(mySetoid)      // => false

Showable

inspect

inspect :: a -> String

inspect returns a string representation of the given value. Useful as a helper function for creating toString methods for ADTs.

import { inspect } from "eek-whales"

inspect("hello world")         // => "hello world"
inspect(42)                    // => "42"
inspect([1, 2, 3])             // => "[1, 2, 3]"
inspect(undefined)             // => "undefined"
inspect(<T>(x: T): T => x)     // => "(x) => x"
inspect(new TypeError("FOO"))  // => "TypeError: FOO"

nodeInspect

nodeInspect :: Symbol

Using nodeInspect in the ADTs allows for defining custom console.log output for Node.js without the need to import the util module. This makes it unnecessary to verify a Node.js environment.

import { inspect, nodeInspect } from "eek-whales"

const Identity = x => ({
  // ...

  toString() {
    return `Identity(${inspect(x)})`
  },

  [nodeInspect]() {
    return this.toString()
  }
})

Number

random

random :: (Number | Undefined) -> Number

A pseudorandom number generator that accepts a seed number as input for reproducible output. By default, the seed is the number returned by Date.now(). The returned floating point number will be between 0 and 1, not including 1; [0, 1). The random number is generated using a linear congruential generator algorithm with the following values:

multiplier (a)	increment (c)	modulus (m)
1103515245	12345	231

import { random } from "eek-whales"

random() // => 0.0469970703125
random() // => 0.871337890625
random() // => 0.1737060546875

random(1001001) // => 0.707733154296875
random(1001001) // => 0.707733154296875

random(0) // => 0
random(1) // => 0.51385498046875