param

Overview

param allow using runtime values from the view/producer to create new paths.

Occasionally, a producer or view need to access a path in state, which depends on a value which is created in the producer itself. param is the path-composition operator to use in such situations.

For example, update.* functions can be given an object in their second argument. Every key in this object can then be referred to with param.<key> in the header

Example

const App: view = ({
  update = update.items[param.foo][param.bar]
}) => (
  <input onChange={e => update(e.target.value,
    { foo: 'state_path', bar: 'yet_another_state_path' }
  )}>
);

It allows moving a lot of complexity of accessing and setting of state, to the path structure; without needing any intermediate state in the view/producer itself.