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In functional programming, a result type is a Monadic type holding a returned value or an error code. They provide an elegant way of handling errors, without resorting to exception handling; when a function that may fail returns a result type, the programmer is forced to consider success or failure paths, before getting access to the expected result; this eliminates the possibility of an erroneous programmer assumption.
- In OCaml, it is defined by the standard library as
type ('a, 'b) result = Ok of 'a | Error of 'b type.
- in Rust, the standard library provides the Result<T,E> type to handle return values or error codes, expanding on the functionality of the Option<T> type.