partialFunction.js

// // 1. Write a function named greet that takes two arguments and logs a greeting:

// function greet(arg1, arg2) {
//   let capitalized = arg1[0].toUpperCase() + arg1.slice(1);
//   console.log(capitalized + ', ' + arg2 + '!');
// }

// greet('howdy', 'Joe');
// greet('good morning', 'Sue');

// function partial(primary, arg1) {
//   return function(arg2) {
//     return primary(arg1, arg2);
//   }
// }

// let sayHello = partial(greet, 'hello');
// sayHello('Brandon');
// let sayHi = partial(greet, 'hi');
// sayHi('Sarah');

// 1. Using partial function application implement a function, sub5, that returns the value of a number subtracted by 5.

// function subtract(a, b) {
//   return a - b;
// }

// function sub5(a) {
//   return subtract(a, 5);
// }

// console.log(sub5(10)); // 5
// console.log(sub5(20)); // 15

// 2. This code is a bit limited however, because we can only subtract by 5. 
// Implement the makeSubN function below so that we can supply any value we want to be subtracted from a, 
// and get a new function that will always subtract this value.

// function subtract(a, b) {
//   return a - b;
// }

// function makeSubN(n) {
//   return function(a) {
//     return subtract(a, n);
//   }
// }

// let sub5 = makeSubN(5);
// console.log(sub5(10)); // 5

// 3. Although the solution above is more flexible, we now want to be able to supply any operation, not just subtraction. 
// Implement makePartialFunc below.

// function makePartialFunc(func, b) {
//   return function(a) {
//     return func(a, b);
//   }
// }

// function multiply(a, b) {
//   return a * b;
// }

// let multiplyBy5 = makePartialFunc(multiply, 5);

// console.log(multiplyBy5(100)); // 500

// 5. Consider the code below: Implement makeMathRollCall such that it returns a partially applied rollCall function, with the subject as 'Math'.

let subjects = {
  English: ['Bob', 'Tyrone', 'Lizzy'],
  Math: ['Fatima', 'Gary', 'Susan'],
  Biology: ['Jack', 'Sarah', 'Tanya'],
};

function rollCall(subject, students) {
  console.log(subject + ':');
  students.forEach(function(student) {
    console.log(student);
  });
}

function makeMathRollCall() {
  return function(students) {
    return rollCall('Math', students);
  }
}

let mathRollCall = makeMathRollCall();
mathRollCall(subjects['Math']);
// => Math:
// => Fatima
// => Gary
// => Susan