Haskell Quine: "ap" Monad
haskell, monads, quine
Solution
Importing `Control.Monad` should give you `ap`. However, in all but the most recent versions of GHC (7.6.1 and newer), you'll also need to import `Control.Monad.Instances` to use the monad instance for functions.
Alternatively, you can import `Control.Applicative` which gives you the `<*>` operator, which is `ap` generalized to `Applicative`, as well as the necessary instances to use it with functions.
Problem
What is the proper way to use the "ap" monad in Haskell? I want to do something similar to this: ``` main = (putStr . ap (++) show) "main = (putStr . ap (++) show) " ``` but I get the error "Not in scope: 'ap'." Using "import Control.Monad" does nothing. And I have tried giving it ``` "ap :: Monad m => m (a -> b) -> m a -> m b" ``` then I get "The type signature for `ap' lacks an accompanying binding"