Some snippets around Lenses

00-no-lenses-simple.js

function update(state) {
  return {
    ...state,
    price: changePrice(state.price)
  };
}

01-no-lenses-complex.js

function update(state) {
  return {
    ...state,
    meta: {
      ...state.meta,
      prices: {
        ...state.meta.prices,
        price: changePrice(state.meta.prices.price)  
      }
    }
  };
}

02-no-lenses-extracted.js

function getPrice(state) {
  return state.meta.prices.price;
}

function setPrice(newPrice, state) {
  return {
    ...state,
    meta: {
      ...state.meta,
      prices: {
        ...state.meta.prices,
        price: newPrice  
      }
    }
  }
}

function update(state) {
  const newPrice = changePrice(getPrice(state));
  return setPrice(newPrice, state);
}

03-no-lenses-generic.js

// getPrice and setPrice

function updateGeneric(getter, setter, fn, state) {
  const newValue = fn(getter(state));
  return setter(newValue, state);
}

function update(state) {
  return updateGeneric(getPrice, setPrice, changePrice, state);
}

04-lens-using-getter-setter.js

// getPrice and setPrice

const lensPrice = L.lens(getPrice, setPrice);

function update(state) {
  return L.modify(lensPrice, changePrice, state);
}

05-lens-basic.js

const lensPrice = ["meta", "prices", "price"];

function update(state) {
  return L.modify(lensPrice, changePrice, state);
}