Re: [Haskell-cafe] Stacking monads

3 Oct 2008

      Andrew Coppin wrote:
...
run_or s0 x y =
   let
     either_rset1 = sequence $ run s0 x
     either_rset2 = sequence $ run s0 y
     either_rset3 = do rset1 <- either_rset1; rset2 <- either_rset2; 
return (merge rset1 rset2)
 in case either_rset3 of
   Left  e    -> throwError e
   Right rset -> lift rset
Do you realise, this single snippet of code utilises the ErrorT monad 
[transformer], the ResultSet monad, *and* the Either monad, all in the 
space of a few lines?? That's three monads in one function! o_O

I scare *myself*, I don't know about you guys...