Simplifying IO in a Purely Functional Language

In a purely functional language, all IO operations are asynchronous by default, removing the need for synchronous IO. Every function that is not async can be considered pure because async is used to handle IO operations, and therefore non-async functions do not perform any IO side effects. By avoiding the use of global variables and mutation, functions can be guaranteed to always return the same value given the same arguments. The absence of mutation also means that functions can be easily cached and memoized.