act.flatten

src/act.gleam

@@ -310,3 +310,13 @@ pub fn try_each(
     })
   }
 }
+
+/// Merges a nested `Action` into a single layer.
+///
+pub fn flatten(action: Action(Action(b, a), a)) -> Action(b, a) {
+  fn(state) {
+    let #(state, action) = action(state)
+    let #(state, result) = action(state)
+    #(state, result)
+  }
+}

test/act_test.gleam

@@ -3,6 +3,8 @@
 
 import gleam/int
 import gleam/io
+import gleeunit
+import gleeunit/should
 
 // The `Action` type and `do` function are imported unqualified since they are
 // so common.
@@ -46,4 +48,11 @@ pub fn main() {
 
   io.println("The result is " <> int.to_string(result))
   io.println("The state is " <> int.to_string(final_state))
+
+  gleeunit.main()
+}
+
+pub fn flatten_test() {
+  act.flatten(fn(ctx) { #(ctx, fn(ctx) { #(ctx, "result") }) })("state")
+  |> should.equal(#("state", "result"))
 }