import { it, assertEq } from 'folktest'
import { Monad } from '../../src/monad.js'

const leftIdentity = (M, a, f) => {
    assertEq(M(a).bind(f), f(a))
}

const rightIdentity = (M, m) => {
    assertEq(m.bind(M), m)
}

const associativity = (m, f, g) => {
    assertEq(m.bind(f).bind(g), m.bind(x => f(x).bind(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', () => {
        const ctr = Monad.bind(undefined, Monad)
        prove(
            ctr,
            ctr(1),
            1,
            x => ctr(x + 1),
            x => ctr(x * 2)
        )
    })
]