JS pattern matching

pattern-matching.js

// fooIsBar :: Int -> String
const fooIsBar = x =>
  x == 1  ?  'one'
: x == 2  ?  'two'
: x == 3  ?  'three'
: x == 4  ?  'four'
: /* or */   'too much'



// sign :: Int -> Int
const sign = x =>
  x  >  0  ?   1
: x === 0  ?   0 
: x  <  0  ?  -1
: /* else */   throw new TypeError('Not an integer')

// take :: Int -> [a] -> [a]
const take = n => xs =>
  xs.length === 0  ?  []
: n === 0          ?  []
: /* otherwise */     [head (xs), ...take (n-1) 
                                          (tail(xs))]

// factorial :: Int -> Int
const factorial = n =>
  n === undefined  ?  0 
: n === 0          ?  1 
: /* otherwise */     n * factorial (n -1)