[Haskell-beginners] How to construct complex string

[Kim-Ee Yeoh]

On Sat, Aug 10, 2013 at 12:41 AM, martin <martin.drautzburg at web.de> wrote:

> > instance Monad Dot where
> >   return a = Dot $ \ uq -> ([],uq,a)
> >   m >>= k  = Dot $ \ uq -> case unDot m uq of
> >                (g1,uq',r) -> case unDot (k r) uq' of
> >                        (g2,uq2,r2) -> (g1 ++ g2,uq2,r2)
>
> I tried to rewrite this using "where" and was bitten badly, because
> inside the "where" uq would not be defined.
>

You could write:

m >>= k = Dot f  where
   f uq = (g1 ++ g2, uq2, r2)  where
      (g1, uq', r) = unDot m uq
      (g2, uq2, r2) = unDot (k r) uq'

Doubtless, there has to be a way of revealing the inner structure, which
looks like some state monad with icing on top.

-- Kim-Ee
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