Roman Numeral Converter

WITH Roman (Numeral) AS
(select 'MCMLXXXVII' as Numeral from dual),
RomToDec (ThisVal, ThisOne, ThisDec, LastDec, Remaining, Pos) AS
(SELECT 0 as ThisVal, cast(null as varchar2(4000)) as ThisOne, 
0 as ThisDec, 0 as LastDec,
Roman.Numeral as Remaining , length(Roman.Numeral) as Pos 
FROM Roman
UNION ALL
SELECT 
case 
  when RomToDec.ThisDec >= RomToDec.LastDec then RomToDec.ThisVal + ThisDec 
  else RomToDec.ThisVal-ThisDec
END as ThisVal, 
substr(RomToDec.Remaining,length(RomToDec.Remaining),1)  as ThisOne, 
case substr(RomToDec.Remaining,length(RomToDec.Remaining),1)  
  when 'M' then 1000
  when 'D' then 500
  when 'C' then 100
  when 'L' then 50
  when 'X' then 10
  when 'V' then 5
  when 'I' then 1
else 0 END as ThisDec,
RomToDec.ThisDec as LastDec,
substr(RomToDec.Remaining,1,length(RomToDec.Remaining)-1) as Remaining,
length(RomToDec.Remaining)-1 as Pos
from RomToDec                           
where Pos >= 0
)
select thisVal
from RomToDec 
where pos is null