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Haskell based parenthesis validator
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| {-| | |
| Module: Validator | |
| Description: Parses parenthesis variations for correct nesting. | |
| Parses (), <>, {}, [] etc for correct nesting, open and closing. | |
| Usage: | |
| $ validator '[<>{()}]' | |
| [<>{()}] | |
| Found valid characters in valid form. | |
| $ validator '[<><><>]' | |
| [<><><>] | |
| Found valid characters in valid form. | |
| $ validator '[(]' | |
| [(] | |
| Valid characters but invalid form. | |
| $ validator '[z]' | |
| [z] | |
| Invalid characters detected, please limit it to ()<>[]{} | |
| -} | |
| module Main where | |
| import System.Environment | |
| import System.Exit | |
| import Data.Map.Strict(assocs, keys, member, Map, fromList, (!?), (!)) | |
| data ErrorCodes = NoError | InvalidInput | Invalid deriving (Show, Eq, Enum) | |
| main :: IO ExitCode | |
| main = do | |
| inputChars <- getArgs | |
| let arg = head inputChars | |
| putStrLn arg | |
| if not (validArg arg) | |
| then do | |
| putStrLn ("Invalid characters detected, please limit it to " ++ validChars) | |
| exitWith (ExitFailure (fromEnum InvalidInput)) | |
| else if validForm arg | |
| then do | |
| putStrLn "Found valid characters in valid form." | |
| exitSuccess | |
| else do | |
| putStrLn "Valid characters but invalid form." | |
| exitWith (ExitFailure (fromEnum Invalid)) | |
| validForm :: String -> Bool | |
| validForm chars | |
| | not ((mod (length chars) 2) == 0) = False -- Not valid as length of input is odd | |
| | otherwise = validFormChecker chars "" -- Begin traversing through characters | |
| validFormChecker :: String -> String -> Bool | |
| -- Recursive validator that adds opening characters to a stack and recurses to validate input. | |
| validFormChecker chars stack | |
| | null stack && null chars = True -- Nothing on the stack and no chars, nothing more to do. | |
| | null chars = False -- If something is on the stack, chars should not be empty. | |
| -- This next line detects if next character is an opening character, adds it to stack and recurses. | |
| | (isOpeningChar (head chars)) && ((validFormChecker (tail chars)) ([(head chars)] ++ stack)) = True | |
| | null stack = False -- This happens when ^^ conditions all have failed and chars is invalid. | |
| | otherwise = (matchingPairs (head chars) (head stack)) && (validFormChecker (tail chars) (tail stack)) | |
| isOpeningChar :: Char -> Bool | |
| -- The keys in `getPairs` are all opening characters. | |
| isOpeningChar currentChar = (currentChar `elem` (keys getPairs)) | |
| matchingPairs :: Char -> Char -> Bool | |
| -- Detect if current character matches the top of the stack. Basically a value lookup in the getPairs map. | |
| matchingPairs char stackTop = (member stackTop getPairs) && (getPairs ! stackTop == char) | |
| validChars :: String | |
| -- Merges all the key value pairs to create a definitive list of valid characters. | |
| validChars = foldr combineChars [] (assocs getPairs) | |
| combineChars :: (Char, Char) -> [Char] -> [Char] | |
| -- Just concatenating characters to a string. | |
| combineChars (char1, char2) keyPair = [char1] ++ [char2] ++ keyPair | |
| getPairs :: Map Char Char | |
| -- The list of valid character pairs. | |
| getPairs = fromList [ ('[', ']') | |
| , ('{', '}') | |
| , ('(', ')') | |
| , ('<', '>') | |
| ] | |
| validArg :: String -> Bool | |
| -- Check all the valid characters by filtering out invalid and comparing the lengths of filtered vs given. | |
| validArg receivedChars = let | |
| vc = validChars | |
| filteredChars = filter (\char -> char `elem` vc) receivedChars | |
| in (length receivedChars) == (length filteredChars) |
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| name: validator | |
| version: 0.1.0.0 | |
| license: BSD3 | |
| license-file: LICENSE | |
| author: Bjorn Tipling | |
| maintainer: bjorn@ambientchill.com | |
| build-type: Simple | |
| cabal-version: >=1.10 | |
| executable validator | |
| main-is: Main.hs | |
| build-depends: base >=4.9 && <4.10, | |
| containers == 0.5.10.2 | |
| hs-source-dirs: . | |
| default-language: Haskell2010 | |
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