hey-redux-you-are-doing-it-wrong.js

// If you haven't already, watch Brian Lonsdorf's "Hey Underscore, You're Doing It Wrong!":
// http://functionaltalks.org/2013/05/27/brian-lonsdorf-hey-underscore-youre-doing-it-wrong/

const { append, eqProps, identity, map, mergeWith, nthArg, pipe, reject, when } = require('Ramda');

const idEquals = eqProps('id');



// Reducers as data-less action function (returns a function that
// takes a state and returns a new state without mutation)

const todo = action => {
  switch(action.type) {
    case 'TODO_UPDATE': {
      return mergeWith(nthArg(0), action.params);
    }
    default: {
      return identity;
    }
  }
};

const todos = action => {
  switch(action.type) {
    case 'TODO_ADD': {
      return append({ id: action.id, text: action.params.text, completed: true });
    }
    case 'TODO_UPDATE': {
      return map(
        when(idEquals(action))(
          todo(action)
        )
      );
    }
    case 'TODO_DELETE': {
      return reject(idEquals(action));
    }
    default: {
      return identity;
    }
  }
};



// Concrete Actions

const addTodo1 = todos({ type: 'TODO_ADD', id: 1, params: { text: 'Foo' } });
const updateTodo1 = todos({ type: 'TODO_UPDATE', id: 1, params: { text: 'Bar', completed: false } });
const deleteTodo0 = todos({ type: 'TODO_DELETE', id: 0 });



// Action plan

const changes = pipe(
  addTodo1,
  updateTodo1,
  deleteTodo0
);



// State changes

const stateBefore = [{ id: 0, text: 'Foo', completed: true }];
const stateAfter = changes(stateBefore);