A Collection of Code Snippets in as Many Programming Languages as Possible

This project is maintained by TheRenegadeCoder

Welcome to the Roman Numeral in Haskell page! Here, you’ll find the source code for this program as well as a description of how the program works.

```
module Main where
import System.Environment
import System.Exit (exitWith, ExitCode(ExitFailure))
asDec :: Char -> Int
asDec 'I' = 1
asDec 'V' = 5
asDec 'X' = 10
asDec 'L' = 50
asDec 'C' = 100
asDec 'D' = 500
asDec 'M' = 1000
asDec _ = -1
romanToDecimal :: String -> Maybe Int
romanToDecimal roman = go roman 0
where go :: String -> Int -> Maybe Int
go [] totals = Just totals
go [a] totals = Just $ totals + (asDec a)
go (a1:a2:as) totals
| (asDec a1) < 1 || (asDec a2) < 1 = Nothing
| (asDec a1) < (asDec a2) = go (a2:as) (totals - (asDec a1))
| otherwise = go (a2:as) (totals + (asDec a1))
main :: IO ()
main = do
args <- getArgs
let roman = head args
if null args then do
putStrLn "Usage: please provide a string of roman numerals"
exitWith $ ExitFailure 1
else do
let intOut = romanToDecimal roman
case intOut of
Nothing -> do
putStrLn "Error: invalid string of roman numerals"
exitWith $ ExitFailure 1
Just x -> putStrLn $ show $ x
```

Roman Numeral in Haskell was written by:

- Parker Johansen

If you see anything you’d like to change or update, please consider contributing.

**Note**: The solution shown above is the current solution in the Sample Programs repository as of Apr 01 2019 03:55:34. The solution was first committed on Oct 21 2018 01:06:56. As a result, documentation below may be outdated.

No ‘How to Implement the Solution’ section available. Please consider contributing.

No ‘How to Run the Solution’ section available. Please consider contributing.