Add new acceptance test scenario: 066

Mutua recursion.

examples/acceptance_tests/066/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/066/aiken.toml

@@ -0,0 +1,3 @@
+name = 'aiken-lang/acceptance_test_066'
+version = '0.0.0'
+description = ''

examples/acceptance_tests/066/lib/tests.ak

@@ -0,0 +1,25 @@
+type Schema {
+  Integer(Int)
+  List(List<Schema>)
+}
+
+fn sum(schema: Schema) -> Int {
+  when schema is {
+    Integer(i) -> i
+    List(xs) -> sum_list(xs)
+  }
+}
+
+fn sum_list(list: List<Schema>) -> Int {
+  when list is {
+    [] -> 0
+    [x, ..xs] -> sum(x) + sum_list(xs)
+  }
+}
+
+test foo() {
+  False
+  // Can't enable the "real" test because it puts the UPLC evaluator in an infinite loop.
+  // -
+  // sum(List([List([Integer(1), Integer(2)]), Integer(3), Integer(4)])) == 10
+}