createState(initialValue, key?)

ts
function createState<T>(initialValue: T, key?: string): Optic<T>;

ts
function createState<T>(initialValue: T, key?: string): Optic<T>;

Creates a global state initialized to the value passed as argument.
Takes a key as an optional string argument. It can be useful when debugging to distinguish between different states.

Returns an optic focused on this state. From this optic we can derive new ones focused on different parts of the state.