useContext should actuallly return not `a`, but `Maybe a`

[srghma]

it's a usual thing to do in js

export function useData() {
  const context = useContext(DataContext)

  if (!context) {
    throw new Error('Missing Data context')
  }

  return data
}

---

Maybe introduce major update to the whole react-basic lib, so that all components carry additional phantom type contexts :: ContextList and top React.render should take empty context?

[megamaddu]

This is intentional. The createContext function in react-basic requires a default value and that value is used when the current React tree doesn't have a value to use from a parent provider.

createContext :: forall a. a -> Effect (ReactContext a)

If you can't provide a useful default value, you can always make your a a Maybe something.

createContext Nothing :: Effect (ReactContext (Maybe yourType))

If you're running into a runtime error here you're most likely using FFI somewhere, such as specifying in PS the context type of a JS React library. In this case it's really important JS's possible edge cases are caught or you've given the context type the actual JS type (often Nullable something, not Maybe something).

[srghma]

oh, sorry, I didn't think about that)

[megamaddu]

No worries, this should be documented better