SKI in MUPL in Racket

mupl-ski.rkt

    (define S (fun "S" "x" (fun #f "y"
                                (fun #f "z"
                                     (call (call (var "x") (var "z"))
                                           (call (var "y") (var "z")))))))
    (define K (fun "K" "x" (fun #f "y" (var "x"))))
    (define I (fun "I" "x" (var "x")))
    
    ;; SKK                                                                                                                                                                                                      
    (define SKK
      (call (call S K) K))
    
    ;; S(K(SI))K                                                                                                                                                                                                
    (define SKIrev
      (call (call S (call K (call S I))) K))
    
    (define SKK2
      (call (call (call SKIrev K) S) K))
    
    (eval-exp (call I (int 2)))
    (eval-exp (call SKK (int 3)))
    (eval-exp (call SKK2 (int 4)))