12.2.1. Promises · Functional Programming in OCamlPromises In Lwt, a promise is a write-once reference: a value that is permitted to mutate at most once. When created, it is like an empty box that contains nothing. We say that the promise is pending. Eventually the promise can be resolved, which is like putting something inside the box. Instead of being resolved, the promise can instead be rejected, in which case the box is filled with an excepti
