Vandise / z

Pattern Matching for Javascript

Pattern matching for Javascript.

Usage

• Install via npm: npm install z
• Require z in your code and use the matches function: const { matches } = require('z')

Avaiable Patterns

• Matches by value: (x = 1) =>, (x = null) =>, (x = 'true') =>
• Matches by object or array: (x = {a: 1}) =>, (x = [1, 2]) =>
• Matches by type: (x = String) =>, (x = Boolean) =>
• Matches by instance: (x = Date) =>, (x = Person) =>
• Matches by splitting array into elements and tail (head, tail) => , (a, b, c, tail) =>, etc…

Examples

• Example: Matches by Object property

const { matches } = require('z')

const person = { name: 'Maria' }
matches(person)(
  (x = { name: 'John' }) => console.log('John you are not welcome!'),
  (x)                    => console.log(`Hey ${x.name}, you are welcome!`)
)

//output: `Hey Maria, you are welcome!`

• Example: Matches by type or instances

const { matches } = require('z')

const result = matches(1)(
  (x = 2)      => 'number 2 is the best!!!',
  (x = Number) => `number ${x} is not that good`,
  (x = Date)   => 'blaa.. dates are awful!'
)

console.log(result) // output: number 1 is not that good

• Example: matches Array content

To match array content you need create multiple arguments for the match function, such as (a, b, c, tail) => {} , then each variable match each item from array. Note: last variable contains all remaining array items, formally named tail. Examples:

const { matches } = require('z')

matches([1, 2, 3, 4, 5])(
  (a, b, c, tail) => 'a = 1, b = 2, c = 3, tail = [4, 5]'  
)

matches([1, 2])(
  (a, tail) => 'a = 1, b = [2]'  
)

matches([1])(
  (a, b,  tail)       => 'Will not match here',
  (a = 2, tail = [])  => 'Will not match here',
  (a = 1, tail = [])  => 'Will match here, tail = []'
)

• Example: Powerful recursive code which will remove sequential repeated items from Array.

Can be mind blowing if it’s the first time you meet pattern matching, but you are gonna understand it!

const { matches } = require('z')

const compress = (numbers) => {
  return matches(numbers)(
    (x, y, xs) => x === y
      ? compress([x].concat(xs))
      : [x].concat(compress([y].concat(xs))),
    (x, [y]) => x === y // stopping condition
      ? [x]
      : [x, y],
    x => x
  )
}

compress([1, 1, 2, 3, 4, 4, 4]) //output: [1, 2, 3, 4]

License

Apache 2.0