add generics

test/fixtures/valid/control.ls

@@ -11,10 +11,10 @@ choose_block: (bit, i32, i32) -> i32: @ (condition: bit, when_true: i32, when_fa
 first_positive: []i32 -> i32?: @ values: []i32 {
     for value in values {
         if value > 0 {
-            return some value
+            return value->|.some
         }
     }
-    nil
+    |.none
 }
 
 labelled_search: []i32 -> i32: @ values: []i32 { loop `outer {