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Task/Remove-duplicate-elements/CafeOBJ/remove-duplicate-elements.cafeobj

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+-- The parametrized module NO-DUP-LIST(ELEMENTS :: TRIV) defines the signature of simple Haskell like list structure.
+-- The removal of duplicates is handled by the equational properties listed after the signature in brackets {}
+-- The binary operation _,_ is associative, commutative, and idempotent.
+-- This list structure does not permit duplicates, they are removed during evaluation (called reduction in CafeOBJ)
+-- Actual code is contained in module called  NO-DUP-LIST.
+-- The tests are performed after opening instantiated NO-DUP-LIST with various concrete types.
+-- For further details see: http://www.ldl.jaist.ac.jp/cafeobj/
+mod! NO-DUP-LIST(ELEMENTS :: TRIV)  {
+    [ List < Elem < Elt]  -- Sorts in Ordered Sorted Algebra
+    op [] : -> List { prec: 0 }  -- Empty List
+    op _,_ : Elt Elt -> Elt { comm assoc idem prec: 80 l-assoc }
+    op [_] : Elt -> List  { prec: 0 }
+}
+
+-- Test on lists of INT, CHARACTER, and STRING
+open NO-DUP-LIST(INT)
+reduce [ 1 , 2 , 1 , 1 ] .     -- Gives [ 1 , 2 ]
+open NO-DUP-LIST(CHARACTER)
+reduce [ 'a' , 'b' , 'a' , 'a' ] .  -- Gives [ 'a' , 'b' ]
+open NO-DUP-LIST(STRING)
+reduce [ "abc" , "def" , "abc" ] . -- Gives [ "def" , "abc" ]