Result type

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.

Examples

• 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.
• Haskell has a type that is sometimes used in a similar way, called Either, which is defined as data Either a b = Left a | Right b.

See also

• Option type
• Exception handling
• Tagged union
• Return type