Test FP-TS A playground to test gcanti's super article. Use case Sentinels Use case: an API that may fail and returns a special value of the codomain Code Test undefined and null Use case: an API that may fail and returns undefined (or null) Code Test Exceptions Use case: an API that may throw Code Test Random values Use case: an API that returns a non deterministic value Code Test Synchronous side effects Use case: an API that reads and/or writes to a global state Code Test Use case: an API that reads and/or writes to a global state and may throw Code Test Asynchronous side effects Use case: an API that performs an asynchronous computation Code ⚠️ I don't know how to test this, help me please :) Use case: an API that performs an asynchronous computation and may reject Code Test