simple-case-expression.js

const Case = cases => (
  pred => (
    (typeof cases[pred] !== 'undefined') ? cases[pred]() : cases['_']()
  )
)

const count = Case({
  0: () => 'zero',
  1: () => 'one',
  _: () => 'many'
})

count(0) // 'zero'
count(1) // 'one'
count(5) // 'many'

const cond = Case({
  true: () => 'yes!',
  false: () => 'no :('
})

cond(true) // 'yes!'
cond(false) // 'no :('

Case({
  1: () => 'a single item',
  _: () => 'many items'
})(2) // 'many items'