integer set1 = new_dict(),
        set2 = new_dict()
setd(3,0,set1)
setd(1,0,set1)
setd(2,0,set1)
setd(5,0,set2)
setd(3,0,set2)
setd(4,0,set2)

function element(object x, integer set)
    return getd_index(x,set)!=0
end function

function u_visitor(object key, object data, object user_data)
    integer {union_set,set2} = user_data
    if set2=0
    or not element(key,union_set) then
        setd(key,data,union_set)
    end if
    return 1
end function

function union(integer set1, integer set2)
integer union_set = new_dict()
    traverse_dict(routine_id("u_visitor"),{union_set,0},set1)
    traverse_dict(routine_id("u_visitor"),{union_set,set2},set2)
    return union_set
end function

function i_visitor(object key, object data, object user_data)
    integer {union_set,set2} = user_data
    if element(key,set2) then
        setd(key,data,union_set)
    end if
    return 1
end function

function intersection(integer set1, integer set2)
integer union_set = new_dict()
    traverse_dict(routine_id("i_visitor"),{union_set,set2},set1)
    return union_set
end function

function d_visitor(object key, object data, object user_data)
    integer {union_set,set2} = user_data
    if not element(key,set2) then
        setd(key,data,union_set)
    end if
    return 1
end function

function difference(integer set1, integer set2)
integer union_set = new_dict()
    traverse_dict(routine_id("d_visitor"),{union_set,set2},set1)
    return union_set
end function

integer res
function s_visitor(object key, object data, object user_data)
    integer set2 = user_data
    if not element(key,set2) then
        res = 0
        return 0 -- cease traversal
    end if
    return 1
end function

function subset(integer set1, integer set2)
    res = 1
    traverse_dict(routine_id("s_visitor"),set2,set1)
    return res
end function

function equality(integer set1, integer set2)
    if dict_size(set1)!=dict_size(set2) then
        return false
    end if
    return subset(set1,set2)
end function

include builtins/map.e -- for keys()

-- matching test code:
?element(3,set1)        -- 1
?element(4,set1)        -- 0
?keys(union(set1,set2)) -- {1,2,3,4,5}
?keys(intersection(set1,set2)) -- {3}
?keys(difference(set1,set2)) -- {1,2}
?subset(set1,set2)      -- 0
integer set3 = new_dict()
setd(2,0,set3)
setd(1,0,set3)
?subset(set3,set1)      -- 1
?equality(set1,set2)    -- 0
setd(3,0,set3)
?equality(set1,set3)    -- 1