path: root/js/match.js

// naive pattern matching
const match = (value, ...patterns) => {
    for (let [pattern, action] of patterns) {
        if (pattern === value || (typeof pattern === 'function' && pattern(value))) {
        return action(value);
        }
    }
    throw new Error("No match found");
}


const isNumber = x => typeof x === 'number';
const isString = x => typeof x === 'string';

const result = match(
  42,
  [1, () => "one"],
  [2, () => "two"],
  [isNumber, x => `number: ${x}`],
  [isString, x => `string: ${x}`]
);

console.log(result);



// slightly fancier pattern matching
const matchObject = (value, ...patterns) => {
    for (let [pattern, action] of patterns) {
        if (typeof pattern === 'function' && pattern(value)) {
            return action(value);
        } else if (typeof pattern === 'object' && pattern !== null) {
            let isMatch = true;
            for (let key in pattern) {
                if (pattern[key] !== value[key]) {
                    isMatch = false;
                    break;
                }
            }
            if (isMatch) return action(value);
        } else if (pattern === value) {
            return action(value);
        }
    }
    throw new Error("No match found");
}

const isAdult = person => person.age >= 18;
const isChild = person => person.age < 18;

const personResult = matchObject(
  { name: 'Rachel', age: 30 },
  [{ name: 'Rachel', age: 30 }, () => "Rachel, 30 years old"],
  [isAdult, person => `${person.name} is an adult`],
  [isChild, person => `${person.name} is a child`]
);

console.log(personResult); 


// Basic Matching: Checking if a value directly matches a pattern.
// Function Patterns: Uses functions to define more complex matching logic.
// Object Patterns: Match objects based on their properties.