\DOC op_U
\TYPE {op_U : ('a -> 'a -> bool) -> 'a list list -> 'a list}
\SYNOPSIS
Takes the union of a list of sets, modulo the supplied relation.
\KEYWORDS
list, set.
\DESCRIBE
An application {op_U eq [l1, ..., ln]} is equivalent to
{op_union eq l1 (... (op_union eq ln-1, ln)...)}. Thus,
every element that occurs in one of the lists will appear in the
result. However, if there are two elements {x} and {y} from different
lists
such that {eq x y}, then only one of {x} and {y} will appear in the
result.
\FAILURE
If an application of {eq} fails when applied to two elements from the
lists.
\EXAMPLE
{
- op_U (fn x => fn y => x mod 2 = y mod 2)
[[1,2,3], [4,5,6], [2,4,6,8,10]];
> val it = [5, 2, 4, 6, 8, 10] : int list
}
\COMMENTS
The order in which the elements occur in the resulting list should
not be depended upon.
High performance set operations may be found in the ML Standard
Basis Library.
There is no requirement that {eq} be recognizable as a kind of
equality (it could be implemented by an order relation, for example).
\SEEALSO
Lib.U, Lib.op_mem, Lib.op_insert, Lib.op_union, Lib.op_mk_set,
Lib.op_intersect, Lib.op_set_diff.
\ENDDOC