Created
December 19, 2011 06:30
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quick NFA using a mock-monadic fold with Set instead of []
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import Data.Set (Set) | |
import qualified Data.Set as S | |
bindSet :: (Ord a, Ord b) => Set a -> (a -> Set b) -> Set b | |
bindSet s k = S.unions . S.toList $ S.map k s | |
foldSet :: (Ord a ) => (a -> b -> Set a) -> a -> [b] -> Set a | |
foldSet _ a [] = S.singleton a | |
foldSet f a (x:xs) = bindSet (f a x) (\fax -> foldSet f fax xs) | |
testNFA :: (Ord q) => NFA q s -> [s] -> Bool | |
testNFA (NFA i a t) = any a . S.toList . foldSet t i | |
data NFA q s = NFA | |
{ intialState :: q | |
, isAccepting :: q -> Bool | |
, transition :: q -> s -> Set q | |
} | |
data State = Q1 | Q2 | Q3 | Q4 | Q5 deriving (Eq, Ord, Show) | |
data Symbol = A | B | C | D deriving (Eq, Ord, Show) | |
-- initial state | |
i = Q1 | |
-- accept criteria | |
a = (`elem` [Q4,Q5]) | |
-- state transitions | |
t Q1 A = S.fromList [Q2] | |
t Q2 A = S.fromList [Q3,Q4] | |
t Q2 B = S.fromList [Q1,Q2] | |
t Q2 C = S.fromList [Q3,Q4] | |
t Q3 D = S.fromList [Q5] | |
t Q4 A = S.fromList [Q2,Q4] | |
t _ _ = S.fromList [] | |
nfa = NFA i a t |
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