separate (Compilation_Unit.Produce_Metrics)
procedure Variant (Current_Compilation_Unit : in out Ada_Compilation_Unit;
                   Program_Unit : in Program_Unit_State_Machine;
                   Halstead : in Halstead_State_Machine;
                   Loc : in Loc_State_Machine;
                   Mccabe : in Mccabe_State_Machine) is

    --========================================================
    -- Variant ::=
    --    "WHEN" Expression { ( "|" | "!" ) Expression } "=>"
    --       Component_List
    --========================================================

    Current_Token : Token_Package.Token;
    No_More_Choices : Boolean := False;

begin
    -- Variant

    Get_Next_Token (Out_Token => Current_Token,
                    From => Current_Compilation_Unit,
                    Current_Loc => Loc);

    if "/=" (Token_Package.Value_Of (Current_Token),
             Token_Package.When_Token) then
        raise Syntax_Error;
    end if;

    -- increment Halstead WHEN operator count
    Halstead.Store_Operator ((Kind => Halstead_Operator.When_Halstead));

    Process_Choices:
        -- repeat for every variant
        loop

            Expression (Current_Compilation_Unit => Current_Compilation_Unit,
                        Program_Unit => Program_Unit,
                        Halstead => Halstead,
                        Loc => Loc,
                        Mccabe => Mccabe,
                        Terminate_Tokens =>
                           Set_Of_Tokens'(Token_Package.Vertical_Bar_Token,
                                          Token_Package.Exclamation_Mark_Token,
                                          Token_Package.Arrow_Token));

            Get_Next_Token (Out_Token => Current_Token,
                            From => Current_Compilation_Unit,
                            Current_Loc => Loc);

            case Token_Package.Value_Of (Current_Token) is

                when Token_Package.Vertical_Bar_Token =>

                    -- increment Halstead VERTICAL_BAR operator count
                    Halstead.Store_Operator
                       ((Kind => Halstead_Operator.Vertical_Bar_Halstead));

                when Token_Package.Exclamation_Mark_Token =>

                    -- increment Halstead EXCLAMATION_MARK operator count
                    Halstead.Store_Operator
                       ((Kind => Halstead_Operator.Exclamation_Mark_Halstead));

                when others =>
                    No_More_Choices := True;

            end case;

            exit Process_Choices when No_More_Choices;

        end loop Process_Choices;

    if "/=" (Token_Package.Value_Of (Current_Token),
             Token_Package.Arrow_Token) then
        raise Syntax_Error;
    end if;

    -- increment Halstead ARROW operator count
    Halstead.Store_Operator ((Kind => Halstead_Operator.Arrow_Halstead));

    Component_List (Current_Compilation_Unit => Current_Compilation_Unit,
                    Program_Unit => Program_Unit,
                    Halstead => Halstead,
                    Loc => Loc,
                    Mccabe => Mccabe);

end Variant;