Re: [Haskell-cafe] Are there standard idioms for lazy, pure error handling?

On Fri, Dec 4, 2009 at 1:14 PM, Jason McCarty wrote:

wren ng thornton wrote:

...

    concat1 :: T a b -> (b -> T a b) -> T a b

This could just as easily be

 concat :: T a b -> (b -> T a c) -> T a c

right? It's a little weird to call this concatenation, but I bet it could come in handy.

T a is, among other things, the free monad for the functor (,) a. The concat you describe is the monadic bind. data T a b = D b | W a (T a b) instance Monad (T a) where return = D D b >>= f = f b W a t >>= f = W a (t >>= f) -- Dave Menendez http://www.eyrie.org/~zednenem/