;; The widening between the two function types is a value the caller builds —
;; a thunk, minted at the call — so there is exactly one place to build it:
;; around the whole argument. Nested inside one, there is no caller standing
;; where the thunk would have to go.
;;
;; The parameter here is (Fn [(Fn [$t] $t)] i32) and taker's address carries
;; (CFn [(CFn [i32] i32)] i32). Admitting that structurally binds $t and then
;; hands one word where the instance declares two, in a position no later pass
;; can widen: the catch-up that builds the outer thunk compares the whole
;; substituted parameter list and this mismatch is inside it. A call with no
;; type variables in it is refused, so this one is too.

(defn taker [h (CFn [i32] i32)] i32 (h 1))

(defn hof [g (Fn [(Fn [$t] $t)] i32)  k $t] i32 (g (fn [x] x)))

(defn main [] i32
  (println (hof taker 0))
  0)