diff options
| -rw-r--r-- | src/gleam/result.gleam | 23 | ||||
| -rw-r--r-- | test/gleam/result_test.gleam | 18 |
2 files changed, 41 insertions, 0 deletions
diff --git a/src/gleam/result.gleam b/src/gleam/result.gleam index 2ebf2ef..76ee0e1 100644 --- a/src/gleam/result.gleam +++ b/src/gleam/result.gleam @@ -202,6 +202,29 @@ pub fn or(first: Result(a, e), second: Result(a, e)) -> Result(a, e) { } } +/// Return the first value if it is Ok, otherwise evaluates the given function for a fallback value. +/// +/// ## Examples +/// +/// > or(Ok(1), Ok(2)) +/// Ok(1) +/// +/// > or(Ok(1), Error("Error 2")) +/// Ok(1) +/// +/// > or(Error("Error 1"), Ok(2)) +/// Ok(2) +/// +/// > or(Error("Error 1"), Error("Error 2")) +/// Error("Error 2") +/// +pub fn lazy_or(first: Result(a, e), second: fn() -> Result(a, e)) -> Result(a, e) { + case first { + Ok(_) -> first + Error(_) -> second() + } +} + /// Combine a list of results into a single result. /// If all elements in the list are Ok then returns an Ok holding the list of values. /// If any element is Error then returns the first error. diff --git a/test/gleam/result_test.gleam b/test/gleam/result_test.gleam index 1c585b5..d047496 100644 --- a/test/gleam/result_test.gleam +++ b/test/gleam/result_test.gleam @@ -119,6 +119,24 @@ pub fn or_test() { |> should.equal(Error("Error 2")) } +pub fn lazy_or_test() { + Ok(1) + |> result.lazy_or(fn() { Ok(2)} ) + |> should.equal(Ok(1)) + + Ok(1) + |> result.lazy_or(fn() { Error("Error 2")} ) + |> should.equal(Ok(1)) + + Error("Error 1") + |> result.lazy_or(fn() { Ok(2)} ) + |> should.equal(Ok(2)) + + Error("Error 1") + |> result.lazy_or(fn() { Error("Error 2")} ) + |> should.equal(Error("Error 2")) +} + pub fn all_test() { [Ok(1), Ok(2), Ok(3)] |> result.all |