Created
September 30, 2017 17:00
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A regular expression matcher using Brzozowski derivatives.
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data Regex | |
= Empty | |
| Single Char | |
| Alt Regex | |
Regex | |
| Con Regex | |
Regex | |
| Star Regex | |
deriving (Show) | |
eStr :: Regex | |
eStr = Star Empty | |
obs :: Regex -> Bool | |
obs Empty = False | |
obs (Single _) = False | |
obs (Alt r s) = obs r || obs s | |
obs (Con r s) = obs r && obs s | |
obs (Star _) = True | |
deriv :: Char -> Regex -> Regex | |
deriv _ Empty = Empty | |
deriv c (Single c') = | |
if c == c' | |
then eStr | |
else Empty | |
deriv c (Alt r s) = Alt (deriv c r) (deriv c s) | |
deriv c (Con r s) = Alt (Con (deriv c r) s) (Con obsR (deriv c s)) | |
where | |
obsR = | |
if obs r | |
then eStr | |
else Empty | |
deriv c (Star r) = Con (deriv c r) (Star r) | |
derivStr :: String -> Regex -> Regex | |
derivStr [] r = r | |
derivStr (a:x) r = derivStr x (deriv a r) | |
match :: Regex -> String -> Bool | |
match r s = obs (derivStr s r) |
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