separate (Compilation_Unit.Produce_Metrics)
procedure If_Statement (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

    --====================================================================
    -- IF_Statement ::=
    --    "IF" Expression "THEN"
    --    Sequence_Of_Statements
    --    { "ELSIF" Sequence_Of_Statements }
    --    [ "ELSE" Sequence_Of_Statements ]
    --    "END" "IF" ";"
    --====================================================================

    Current_Token : Token_Package.Token;

begin
    -- IF_Statement

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

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

    -- increment McCabe PI
    Mccabe.Change_Pi;

    -- until "THEN" is found
    Expression (Current_Compilation_Unit => Current_Compilation_Unit,
                Program_Unit => Program_Unit,
                Halstead => Halstead,
                Loc => Loc,
                Mccabe => Mccabe,
                Terminate_Tokens =>
                   Set_Of_Tokens'(1 => Token_Package.Then_Token));

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

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

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

    Process_Elsifs:
        while Token_Package.Value_Of (Peek (From => Current_Compilation_Unit)) =
                 Token_Package.Elsif_Token loop

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

            -- increment Halstead ELSIF_THEN operator count
            Halstead.Store_Operator
               ((Kind => Halstead_Operator.Elsif_Then_Halstead));

            -- increment McCabe PI
            Mccabe.Change_Pi;

            -- until "THEN" is found
            Expression (Current_Compilation_Unit => Current_Compilation_Unit,
                        Program_Unit => Program_Unit,
                        Halstead => Halstead,
                        Loc => Loc,
                        Mccabe => Mccabe,
                        Terminate_Tokens =>
                           Set_Of_Tokens'(1 => Token_Package.Then_Token));

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

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

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

        end loop Process_Elsifs;

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

    if Token_Package.Value_Of (Current_Token) = Token_Package.Else_Token then

        -- increment Halstead ELSE operator count
        Halstead.Store_Operator ((Kind => Halstead_Operator.Else_Halstead));

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

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

    end if;

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

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

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

    -- increment Halstead IF_THEN_END_IF operator count
    Halstead.Store_Operator ((Kind =>
                                 Halstead_Operator.If_Then_End_If_Halstead));

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

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

    -- increment Halstead SEMICOLON operator count
    Halstead.Store_Operator ((Kind => Halstead_Operator.Semicolon_Halstead));

end If_Statement;