import { it, assert } from 'folktest'
import { Option, Result } from '../../src/index.js'

const leftIdentity = (M, a, f) => {
  assert(M(a).chain(f).equals(f(a)))
}

const rightIdentity = (M, m) => {
  assert(m.chain(M).equals(m))
}

const associativity = (m, f, g) => {
  assert(m.chain(f).chain(g).equals(m.chain(x => f(x).chain(g))))
}

export const prove = (M, m, a, f, g) => {
  leftIdentity(M, a, f)
  rightIdentity(M, m)
  associativity(m, f, g)
}

export const Tests = [
  it('should adhere to monadic laws', () => {
    [Option, Result].forEach(F => {
      const Ctr = F.of

      prove(
        Ctr,
        Ctr(1),
        1,
        x => Ctr(x + 1),
        x => Ctr(x * 2)
      )
    })
  })
]