Using the abstraction

Now your Set4.purs module has fairly decent set of abstract tools all built on the Monad interface. Now go back through sets 1, 2, and 3 and redo them all using the library of functions you built up in Set4.purs. Since Gen is now a newtype you will have to make some changes to the functions that use it. This may seem like a waste of time, but it will develop your familiarity with the names actually used* by PureScript’s monad library. This is the core of developing a working knowledge of monads. The first three sets were the motivation. Now we’re getting to the real world use.

* This is a lie. Unlike Haskell, sequence is part of Data.Traversable, and PureScript’s monad libraries don’t have liftM2 and liftM3. Instead, you could use lift2 and lift3 from Apply (in Control.Apply), which is a superclass of Monad, or you might rewrite using <$> and <*>. Also, pure is actually a member of Applicative, but these Monad Challenges were originally written for Haskell and asked the reader to implement return and bind for their Monad instances. In Haskell, for path-dependent reasons, return is a member of Monad and is equivalent to pure, as of the adoption of the Haskell 2014 Applicative => Monad proposal, when Applicative became a superclass of Monad in Haskell as well (implemented in GHC 7.10). In current versions of Haskell, pure from Applicative provides the default implementation of return in Monad instances.

Previous Page - Next Page