content: // @flow
  
  import React from 'react';
  
  React.useState(); // Error: function requires another argument.
  
  const [count, setCount] = React.useState<number>(1);
  
  (count: number); // Ok
  (count: string); // Error: number is incompatible with string
  
  setCount(2); // Okay
  setCount(true); // Error: boolean is incompatible with number
  