Fibonacci |> CPS |> defunctionalization |> TCO |> defunctionalization

fib_cps_defun.js

//const lam1_fun = (n, k) => x => fib_cps((n-2), lam2_fun(x, k))
const lam1_def = (n, k) => ({
    tag: 'lam1',
    n: n,
    k: k
})

//const lam2_fun = (x, k) => y => k(x+y)
const lam2_def = (x, k) => ({
    tag: 'lam2',
    x: x,
    k: k
})

const id_def = ({
    tag: 'id'
})

const apply_thunk = (f, x) => ({
    thunk_tag: 'apply',
    f: f,
    x: x
})

const apply = (f, x) =>{    
    switch (f.tag) {
        case 'lam1':
            return fib_thunk((f.n-2), lam2_def(x, f.k));
            
        case 'lam2':            
            return apply_thunk(f.k, f.x + x);        

        case 'id':
            return x;
            
    }
}

const fib_thunk = (n, k) => ({
    thunk_tag: 'fib',
    n: n,
    k: k
})

const fib_def = (n, k) => {    
    switch(n){
        case 0:
            return apply_thunk(k, 0);
        case 1:
            return apply_thunk(k, 1);
        default:
            return fib_thunk((n-1), lam1_def(n, k));
    }
}

const eval = t => {
    switch(t.thunk_tag){
        case 'apply':
            return apply(t.f, t.x);
        case 'fib':
            return fib_def(t.n, t.k);
    }
}

const tco_def = (t) => {

    while(t.thunk_tag) {
        //console.log(JSON.stringify(t))
        t = eval(t);
    }

    return t;
};

console.log(tco_def(fib_def(5, id_def)))