a-tale-of-numbers-and-functions

a-tale-of-numbers-and-functions.js

const zero = F => V => V;
const one = F => V => F(V);
const two = F => V => F(F(V));
const three = F => V => F(F(F(V)));

const add = N => M => F => V => N(F)(M(F)(V));
const multiply = N => M => F => V => N(M(F))(V);
const power = N => M => F => V => (M(N))(F)(V);

const successor = N => F => V => F(N(F)(V));
const predecessor = N => F => V => N(g => h => h(g(F)))(u => V)(u => u);

let trackerFuncCallCount = 0;

const trackerFunc = () => {
  trackerFuncCallCount++; // increments for each function call
}

// ! ONLY RUN ONE OF THE BELOW FUNCTION CALLS AT A TIME. 
// Else, you'll mess with trackerFuncCallCount. 
// So, just uncomment one function call and run the code.

// zero(trackerFunc)(); // trackerFuncCallCount => 0
// one(trackerFunc)(); // trackerFuncCallCount => 1
// two(trackerFunc)(); // trackerFuncCallCount => 2
// three(trackerFunc)(); // trackerFuncCallCount => 3

// add(one)(two)(trackerFunc)(); // trackerFuncCallCount => 3
// add(three)(three)(trackerFunc)(); // trackerFuncCallCount => 6

// multiply(one)(two)(trackerFunc)(); // trackerFuncCallCount => 2
// multiply(three)(three)(trackerFunc)(); // trackerFuncCallCount => 9

// power(one)(two)(trackerFunc)(); // trackerFuncCallCount => 1
// power(three)(three)(trackerFunc)(); // trackerFuncCallCount => 27

// successor(one)(trackerFunc)(); // trackerFuncCallCount => 2
// successor(three)(trackerFunc)(); // trackerFuncCallCount => 4
// successor(successor(one))(trackerFunc)(); // trackerFuncCallCount => 3

// predecessor(one)(trackerFunc)(); // trackerFuncCallCount => 0
// predecessor(three)(trackerFunc)(); // trackerFuncCallCount => 2
// predecessor(predecessor(three))(trackerFunc)(); // trackerFuncCallCount => 1

console.log(trackerFuncCallCount);