Add new acceptance test scenario: 054.

**a**

  ```
  × Main thread panicked.
  ├─▶ at crates/uplc/src/optimize.rs:16:68
  ╰─▶ called `Result::unwrap()` on an `Err` value: FreeUnique(Name { text: "__other_clauses_delayed", unique: Unique(13) })
  ```

  **b**

  ```
  × Main thread panicked.
  ├─▶ at crates/aiken-lang/src/builder.rs:771:14
  ╰─▶ not yet implemented: Assign
  ```

  **c**

  ```
  × choice_4 failed
  help: ┍━ left ━━━━━━━━━━━━━┑
        │ (con data #d87a80) │
        ┕━━━━━━━━━━━━━━━━━━━━┙

        should be equal to

        ┍━ right ━━━━━━━━━━━━━━━━━━┑
        │ (con data #d8799f182aff) │
        ┕━━━━━━━━━━━━━━━━━━━━━━━━━━┙
  ```

examples/acceptance_tests/056/aiken.lock

@@ -0,0 +1,5 @@
+# This file was generated by Aiken
+# You typically do not need to edit this file
+
+requirements = []
+packages = []

examples/acceptance_tests/056/aiken.toml

@@ -0,0 +1,3 @@
+name = "aiken-lang/acceptance_test_056"
+version = "0.0.0"
+dependencies = []

examples/acceptance_tests/056/lib/choice_a.ak

@@ -0,0 +1,24 @@
+// Could possibly be forbidden by the parser instead if we have no intent to support that.
+pub fn choice(self: List<Option<a>>) -> Option<a> {
+  when self is {
+    [] -> None
+    [Some(_) as result, ..] -> result
+    [None, ..others] -> choice(others)
+  }
+}
+
+test choice_1() {
+  choice([Some(14), Some(42)]) == Some(14)
+}
+
+test choice_2() {
+  choice([]) == None
+}
+
+test choice_3() {
+  choice([None]) == None
+}
+
+test choice_4() {
+  choice([None, Some(42)]) == Some(42)
+}

examples/acceptance_tests/056/lib/choice_b.ak

@@ -0,0 +1,23 @@
+pub fn choice(self: List<Option<a>>) -> Option<a> {
+  when self is {
+    [] -> None
+    [Some(x), ..] -> Some(x)
+    [None, ..others] -> choice(others)
+  }
+}
+
+test choice_1() {
+  choice([Some(14), Some(42)]) == Some(14)
+}
+
+test choice_2() {
+  choice([]) == None
+}
+
+test choice_3() {
+  choice([None]) == None
+}
+
+test choice_4() {
+  choice([None, Some(42)]) == Some(42)
+}

examples/acceptance_tests/056/lib/choice_c.ak

@@ -0,0 +1,23 @@
+pub fn choice(self: List<Option<a>>) -> Option<a> {
+  when self is {
+    [] -> None
+    [None, ..others] -> choice(others)
+    [result, ..] -> result
+  }
+}
+
+test choice_1() {
+  choice([Some(14), Some(42)]) == Some(14)
+}
+
+test choice_2() {
+  choice([]) == None
+}
+
+test choice_3() {
+  choice([None]) == None
+}
+
+test choice_4() {
+  choice([None, Some(42)]) == Some(42)
+}