[Haskell-cafe] Re: Search monad

Edsko de Vries wrote:

Hey,

I have a structure containing Xs in various places, like so

data X data Structure = Structure .. [X] .. [X] ..

And I defined mapStructure

mapStructure :: (X -> X) -> (Structure -> Structure)

I then wanted to use mapStructure to define queries as well as transformations on structures. I generalized mapStructure to mapStructureM:

mapStructure :: Monad m => (X -> m X) -> (Structure -> m Structure)

I guess you want an applicative functor. See also http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Traversable.html and the accompanying papers. Regards, apfelmus