1 files changed, 114 insertions, 0 deletions
diff --git a/src/result.gleam b/src/result.gleam
new file mode 100644
index 0000000..996d92a
--- /dev/null
+++ b/src/result.gleam
@@ -0,0 +1,114 @@
+import assert
+
+doc """
+Result represents the result of something that may succeed or fail.
+`Ok` means it was successful, `Error` means it failed.
+"""
+pub enum Result(error, value) =
+  | Ok(value)
+  | Error(error)
+;
+
+import Result:*
+
+pub fn is_ok(result) {
+  case result {
+  | Error(_) => False
+  | Ok(_) => True
+  }
+}
+
+test is_ok {
+  is_ok(Ok(1)) |> assert:true
+  is_ok(Error(1)) |> assert:false
+}
+
+pub fn is_error(result) {
+  case result {
+  | Ok(_) => False
+  | Error(_) => True
+  }
+}
+
+test is_error {
+  is_error(Ok(1)) |> assert:false
+  is_error(Error(1)) |> assert:true
+}
+
+pub fn map(result, fun) {
+  case result {
+  | Ok(x) => fun(x)
+  | Error(_) => result
+  }
+}
+
+test map {
+  Ok(1)
+    |> map(_, fn(x) { x + 1 })
+    |> assert:equal(_, Ok(2))
+  Error(1)
+    |> map(_, fn(x) { x + 1 })
+    |> assert:equal(Error(1))
+}
+
+pub fn map_error(result, fun) {
+  case result {
+  | Ok(_) => result
+  | Error(error) => Error(fun(error))
+  }
+}
+
+test map_error {
+  Ok(1)
+    |> map_error(_, fn(x) { x + 1 })
+    |> assert:equal(_, Ok(1))
+  Error(1)
+    |> map_error(_, fn(x) { x + 1 })
+    |> assert:equal(_, Error(2))
+}
+
+pub fn flatten(result) {
+  case result {
+  | Ok(x) => x
+  | Error(_) => result
+  }
+}
+
+test flatten {
+  flatten(Ok(Ok(1)))
+    |> assert:equal(_, Ok(1))
+  flatten(Ok(Error(1)))
+    |> assert:equal(_, Error(1))
+  flatten(Error(1))
+    |> assert:equal(_, Error(1))
+}
+
+pub fn flat_map(result, fun) {
+  result
+    |> unwrap(_, fun)
+    |> flatten
+}
+
+test flat_map {
+  Error(1)
+    |> flat_map(_, fn(x) { Ok(x + 1) })
+    |> assert:equal(_, Error(1))
+  Ok(1)
+    |> flat_map(_, fn(x) { Ok(x + 1) })
+    |> assert:equal(_, Ok(2))
+  Ok(1)
+    |> flat_map(_, fn(_) { Error(1) })
+    |> assert:equal(_, Error(1))
+}
+
+pub fn unwrap(result, default) {
+  case result {
+  | Ok(v) => v
+  | Error(_) => default
+  }
+}
+
+test unwrap {
+  unwrap(Ok(1), 50) |> assert:equal(_, 1)
+  unwrap(Error("nope"), 50) |> assert:equal(_, 50)
+}