monads

I am new at haskell, I have to write a program context-aware,so I thought I can use the Reader Monad for keeping the context read from a file, I know how to read the file puting the content in a list of tuplessomething like [([Char],[Char])], but I do not know how to implement the Reader Monad for making the environment available to all the components of my program without using imperative style, In particular I do not know how to set and use the environment, as far as I understood I should give it as parameter to all the functions that need the environment with runReader function env, but I

I am currently studying the bonds between monad and applicative functors. I see two implementation for ap: ap m1 m2 = do { f <- m1 ; x <- m2 ; return (f x) } and ap m1 m2 = do { x <- m2 ; f <- m1 ; return (f x) } The second one is different, yet, would it be a good implementation for <*> ? I got lost in the proof of pure (.) <*> u <*> v <*> w = u <*> (v <*> w) I try to get an intuition of "what part of the monad is the applicative functor"... There are at least three relevant aspects to this question. Given a Monad m instance, what is the specification of its necessary Applicative m superclass

In order to better understand monad transformers I implemented one. Since Javascript is dynamically typed I don't mimic type or data constructors but declare only plain old Javascript objects, which hold the corresponding static functions to form a specific monad / transformer. The underlying idea is to apply these methods to a value/values in a container type. Types and containers are separated so to speak. Array s can contain any number of elements. It is trivial to extend Array s so that they implement the monad interface. Array s can also represent the two variants of the maybe type. An

After a previous question on stackoverflow regarding async / await it seemed to me that await was much more powerful and general than the marketing suggested. It seems to be a general method of building computation expressions just like in F#. So after a bit of a struggle I came up with some code that successfully executes as below. using FluentAssertions; using System.Collections.Generic; namespace EnumerableViaAwait.Specs { [global::Microsoft.VisualStudio.TestTools.UnitTesting.TestClass] public class MyTestClass { public IEnumerable<int> Numbers() { return EnumeratorMonad.Build<int>(async

I have two functions, one that tries to get a token from a webservice and may fail, and one that tries to use this token to get the username and may fail. getToken :: IO (Maybe Token) getUsername :: Token -> IO (Maybe String) I would like to take the result of getToken and feed it to getUsername . If there was only IO or Maybe , I could simply use bind, but since there are down nested monads, I can't. How can I write something equivalent to getToken >>= getUsername :: IO (Maybe String) ? More generally, what function has type m1 m2 a -> (a -> m1 m2 b) -> m1 m2 b ? Bonus question: how would I