op_insert

Lib.op_insert ('a -> 'a -> bool) -> 'a -> 'a list -> 'a list

Add an element to a list if it is not already there.

If there exists an element y in list, such that eq x y, then insert eq x list equals list. Otherwise, x is added to list.

Failure

Never fails.

Example

- op_insert (fn x => fn y => x = y mod 2) 1 [3,2];
> val it = [3, 2] : int list

- op_insert aconv (Term `\x. x /\ y`)
                  [T, Term `\z. z /\ y`, F];
> val it = [`T`, `\z. z /\ y`, `F`] : term list

- op_insert aconv (Term `\x. x /\ y`)
                  [T, Term `\z. z /\ a`, F];
> val it = [`\x. x /\ y`, `T`, `\z. z /\ a`, `F`] : term list

Comments

There is no requirement that eq be recognizable as a kind of equality (it could be implemented by an order relation, for example).

One should not write code that depends on the arrangement of elements in the result.

A high-performance implementation of finite sets may be found in structure HOLset.

See also

Lib.insert, Lib.op_mem, Lib.op_union, Lib.op_mk_set, Lib.op_U, Lib.op_intersect, Lib.op_set_diff