XO0203: success of a Result typed T must be written Ok(x)

error · reported by the checker

In a function declared -> T ! E, a returned T means success and a returned Result[T, E] is passed through as is. When T is itself a Result, a returned Result would be ambiguous, so success must be written Ok(x) explicitly. The same applies to closures whose results are collected, as in xs.map(fn(x) { Ok(g()) }). See core 2.6.

Example

enum E { A }

fn f(r: Result[Int, Str]) -> Result[Int, Str] ! E { r }

Fix

enum E { A }

fn f(r: Result[Int, Str]) -> Result[Int, Str] ! E { Ok(r) }

Run xo explain XO0203 for this text in a terminal, or see section 10.6 of the specification.

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Reference

XO0203: success of a Result typed T must be written Ok(x)

Example

Fix