1. a unary :: operator for binding methods to their objects: `foo.then(::console.log)`
2. a binary :: operator for chaining: `x(a)::y(b)` (equivalent to `y.call(x(a), b)`)
1. a unary :: operator for binding methods to their objects: `foo.then(::console.log)`
2. a binary :: operator for chaining: `x(a)::y(b)` (equivalent to `y.call(x(a), b)`)