===========
Application
===========

foo (A B : *) (f : A -> B) (x : A) := 
    (fun (x : B) => x) (f x);

---
(program
  (definition
    (identifier)
    (param_block
      (identifier)
      (identifier)
      (expr
        (app_term
          (app
            (term
              (star))))))
    (param_block
      (identifier)
      (expr
        (arrow
          (app_term
            (app
              (term
                (identifier))))
          (expr
            (app_term
              (app
                (term
                  (identifier))))))))
    (param_block
      (identifier)
      (expr
        (app_term
          (app
            (term
              (identifier))))))
    (expr
      (app_term
        (app
          (term
            (expr
              (app_term
                (labs
                  (param_block
                    (identifier)
                    (expr
                      (app_term
                        (app
                          (term
                            (identifier))))))
                  (expr
                    (app_term
                      (app
                        (term
                          (identifier)))))))))
          (term
            (expr
              (app_term
                (app
                  (term
                    (identifier))
                  (term
                    (identifier)))))))))))