church numerals

church.js

function church(n){
    return function(f){
        return function(x){
            let res = x
            for(let i=0;i<n;i++){
                res = f(res)
            }
            return res
        }
    }
}
function unchurch(cn){
    return cn(function(x){return x+1})(0)
}

const succ = function(n){
    return function(f){
        return function(x){
            let t1 = n(f)
            let t2 = t1(x)
            let t3 = f(t2)
            return t3
        }
    }
}

const plus = function(m){
    return function(n){
        let t1 = n(succ)
        let t2 = t1(m)
        return t2
    }
}

const mult = function(m){
    return function(n){
        return function(f){
            let t1 = n(f)
            return m(t1)
        }
    }
}

const pred = function(n){
    return function(f){
        return function(x){
            let t1 = function(g){
                return function(h){
                    let t1 = g(f)
                    return h(t1)
                }
            }
            let t2 = function(u){
                return x
            }
            let t3 = function(u){
                return u
            }
            let t4 = n(t1)
            let t5 = t4(t2)
            let t6 = t5(t3)
            return t6

        }
    }
}

const minus = function(m){
    return function(n){
        let t1 = n(pred)
        return t1(m)
    }
}

let zero = church(0)
let one = succ(zero)
let two = church(2)
let three = plus(one)(two)
let nine = mult(three)(three)
let seven = pred(church(8))
let four = minus(church(10))(church(6))
console.log(unchurch(one))
console.log(unchurch(three))
console.log(unchurch(nine))
console.log(unchurch(seven))
console.log(unchurch(four))