(type u32 (primitive u32))
(type A (enum (A1 (x u32)) (A2 (x u32))))
(type B (enum (B1 (x u32)) (B2 (x u32))))

(decl Input (A) u32)
(extractor Input get_input) ;; fn get_input<C>(ctx: &mut C, ret: u32) -> Option<(A,)>

(decl Lower (A) B)

(rule
  (Lower (A.A1 sub @ (Input (A.A2 42))))
  (B.B2 sub))

(decl Extractor (B) A)
(rule
  (A.A2 x)
  (Extractor (B.B1 x)))

(rule
  (Lower (Extractor b))
  b)