Add DFA and NFA representations

src/Rextra/Dfa.hs

@@ -0,0 +1,36 @@
+module Rextra.Dfa where
+-- TODO don't export internals
+
+import qualified Data.Map.Strict as Map
+import qualified Data.Set as Set
+
+data State s t = State
+  { transitions       :: Map.Map t s
+  , defaultTransition :: s
+  , accepting         :: Bool
+  }
+
+data Dfa s t = Dfa
+  { dfaStates     :: Map.Map s (State s t)
+  , dfaEntryState :: s
+  }
+
+{-
+ - Constructing and modifying a DFA
+ -}
+
+-- TODO
+
+{-
+ - "Executing" a DFA
+ -}
+
+getState :: (Ord s) => Dfa s t -> s -> State s t
+getState dfa s = dfaStates dfa Map.! s
+
+transition :: (Ord s, Ord t) => Dfa s t -> s -> t -> s
+transition dfa s t =
+  let state = getState dfa s
+  in  case transitions state Map.!? t of
+        (Just nextState) -> nextState
+        Nothing          -> defaultTransition state