Hmm, I'm still having trouble implementing local for the MonadReader instance of M.

On Thu, Oct 31, 2013 at 11:59 AM, Nickolay Kudasov <nickolay.kudasov@gmail.com> wrote:

Hi David,

I believe the easiest way to do what you want is to use MonadReader class instead of explicit t (Reader [String] a):

push' :: MonadReader [String] m => String -> m a -> m a
push' s = local (s:)

Best,
Nick

2013/10/31 David Fox <dsf@seereason.com>

I can write a stack push function in the reader monad like so:

    import Control.Monad.Reader

    push :: String -> Reader [String] a ->  Reader [String] a

    push s action = local (s :) action

How can I write a push that works inside a monad transformer?

    push' :: MonadTrans t => String -> t (Reader [String]) a ->  t (Reader [String]) a

    push' s action = ???

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