Haskell <<loop>> Exception

Question

I'm getting a <<loop>> Exception for my State Monad instance and I suppose this refers to an infinite loop, however I don't see how my code could lead to one upon use:

instance Monad (State' s) where

    -- return :: a -> State' s a
    return x = State' (\(s,c) -> (x, s, (c <> oneReturn) ))

    -- (>>=) :: State' s a -> (a -> State' s b) -> State' s b
    st >>= k = State' $ \(s,c) -> let (a, s', c) = runState' st (s,c)
                                  in runState' (k a) (s',(c <> oneBind) )

instance MonadState (State' s) s where

    -- get :: State' s s
    get = State' $ \(s,c) -> (s,s, (c <> oneGet))

    -- put :: s -> State' s ()
    put s = State' $ \(_,c) -> ((),s, (c <> onePut))

If anyone has a clue and could help me out it's much appreciated!

Best regards, Skyfe.

EDIT: For reference the one<SomeMonadicFunc> are for increasing the counter properly when bound with a current Counts value -

oneBind   = Counts 1 0 0 0
oneReturn = Counts 0 1 0 0
oneGet    = Counts 0 0 1 0
onePut    = Counts 0 0 0 1

You may not remove your content in this manner. It is wholly unfair to the people who spent time and effort answering your question. As for other students committing "fraud"; If it was not "fraud" for you to post here in the first place, how could it be fraud for others to also use the same information? — Andrew Barber
– Andrew Barber, Commented Oct 19, 2014 at 19:44

leftaroundabout · Accepted Answer · 2014-10-15 12:50:48Z

5

        let (a, s', c) = runState' st (s,c)

This is a recursive definition: the c in the result is used to compute the result, which is used to...

You probably mean let (a,s',c') = runState' st (s,c) in runState' (k a) (s',(c' <> oneBind) ), without the shadowed c variable.

answered Oct 15, 2014 at 12:50

leftaroundabout

121k6 gold badges185 silver badges337 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user2999349 Over a year ago

That fixed it indeed, I hadn't noticed it, thank you! The difference one ' accent can make hah.

Collectives™ on Stack Overflow

Haskell <<loop>> Exception

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related