Intro_composable_functional.js

// Identity functor
const Box = x => ({
  map: f => Box(f(x)),
  fold: f => f(x),
  inspect: () => `Box(${x})`
});

// const Either = Right || Left

const Right = x => ({
  chain: f => f(x),
  map: f => Right(f(x)),
  fold: (f, g) => g(x),
  inspect: () => `Right(${x})`
});

const Left = x => ({
  chain: f => Left(x),
  map: f => Left(x),
  fold: (f, g) => f(x),
  inspect: () => `Left(${x})`
});

const fromNullable = x => x != null ? Right(x) : Left(x));
const tryCatch = f => {
  try { 
    return Right(f());
  }
  catch(e) { 
    return Left(e);
  }
}

// Semigroups
const All = x => ({
  x,
  concat: ({ x: y }) => All(x && y),
  inspect: () => `All(${x})`;
});
const First = x => ({
  x,
  concat: _ => First(x),
  inspect: () => `First(${x})`
})