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data FSM state input output = FSM        -- Input and output alphabet are constricted at compile time by datatype
  { start  :: state                      -- Start state
  , trans  :: state -> input -> state    -- Transition function
  , accept :: [state]                    -- Set of accept states
  , out    :: OutFunc state input output -- Output function, either Moore or Mealy
  }
 
data OutFunc state input output
  = Moore (state -> output)
  | Mealy (state -> input -> output)
 
runFSM :: Eq state => FSM state input output -> [input] -> (state, Bool)
runFSM (FSM start trans accept out) inputs = (finalState, elem finalState accept)
  where
    -- finalState = foldl' trans start input
    finalState = go inputs start
 
    -- Output only changes when state changes occur
  --go :: [input] -> state -> state
    go []     acc = acc
    go (x:xs) currentState = go xs (trans currentState x)
 

prog.c:2:1: error: unknown type name ‘data’
 data FSM state input output = FSM        -- Input and output alphabet are constricted at compile time by datatype
 ^~~~
prog.c:2:10: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘state’
 data FSM state input output = FSM        -- Input and output alphabet are constricted at compile time by datatype
          ^~~~~
prog.c:2:10: error: unknown type name ‘state’
prog.c:9:1: error: unknown type name ‘data’
 data OutFunc state input output
 ^~~~
prog.c:9:14: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘state’
 data OutFunc state input output
              ^~~~~
prog.c:9:14: error: unknown type name ‘state’
prog.c:16:26: warning: missing terminating ' character
     -- finalState = foldl' trans start input
                          ^
prog.c:16:26: error: missing terminating ' character
     -- finalState = foldl' trans start input
                          ^~~~~~~~~~~~~~~~~~~

Standard output is empty