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(.using
 [library
  [lux "*"
   ["_" test {"+" Test}]
   [abstract
    [equivalence {"+" Equivalence}]
    [monad {"+" do}]]
   [control
    ["[0]" function]]
   [math
    ["[0]" random]
    [number
     ["n" nat]]]]]
 [\\library
  ["[0]" / {"+" Functor}]])

(type: .public (Injection f)
  (All (_ a) (-> a (f a))))

(type: .public (Comparison f)
  (All (_ a)
    (-> (Equivalence a)
        (Equivalence (f a)))))

(def: (identity injection comparison (open "@//[0]"))
  (All (_ f) (-> (Injection f) (Comparison f) (Functor f) Test))
  (do [! random.monad]
    [sample (# ! each injection random.nat)]
    (_.test "Identity."
            ((comparison n.=)
             (@//each function.identity sample)
             sample))))

(def: (homomorphism injection comparison (open "@//[0]"))
  (All (_ f) (-> (Injection f) (Comparison f) (Functor f) Test))
  (do [! random.monad]
    [sample random.nat
     increase (# ! each n.+ random.nat)]
    (_.test "Homomorphism."
            ((comparison n.=)
             (@//each increase (injection sample))
             (injection (increase sample))))))

(def: (composition injection comparison (open "@//[0]"))
  (All (_ f) (-> (Injection f) (Comparison f) (Functor f) Test))
  (do [! random.monad]
    [sample (# ! each injection random.nat)
     increase (# ! each n.+ random.nat)
     decrease (# ! each n.- random.nat)]
    (_.test "Composition."
            ((comparison n.=)
             (|> sample (@//each increase) (@//each decrease))
             (|> sample (@//each (|>> increase decrease)))))))

(def: .public (spec injection comparison functor)
  (All (_ f) (-> (Injection f) (Comparison f) (Functor f) Test))
  (<| (_.for [/.Functor])
      ($_ _.and
          (..identity injection comparison functor)
          (..homomorphism injection comparison functor)
          (..composition injection comparison functor)
          )))