Remove duplicate elements: Difference between revisions

=={{header|CafeOBJ}}==

The parametrized module NO-DUP-LIST(ELEMENTS :: TRIV) defines the signature of a space separated list structure. The removal of duplicates is handled by the equational properties listed after the signature in brackets {}. There is no user written code in module NO-DUP-LIST. The binary operation (_ _) is associative, commutative, and idempotent, meaning (x , x) = x. This list structure does not permit duplicates, they are removed during evaluation (called reduction in CafeOBJ). Using this module we can perform set union, just by evaluating two lists e.g:

--> (4 5 1 2 3):Int

 

 

 

mod! NO-DUP-LIST(ELEMENTS :: TRIV) {

op __ : Elt Elt -> Elt { comm assoc idem assoc }

reduce "abc" "def" "abc" "abc" "abc" .

close

 

'''How does work?'''

The evaluation automatically uses right associativity. So starting with:

 

 

The system places appropriate brackets on the entire expression:

 

 

Idempotency is applied at rightmost inner brackets:

We get rewrite ''(1 1) -> 1''. The term is now:

 

Any further occurrence of 1 will be removed.

We get rewrite ''(1 2) -> 2 ''. The term is now:

 

 

By already established idempotency we finally get

 

 

=={{header|Ceylon}}==