emir burak In Informatics, there are two (related) meanings of the word "monad": * A triple (T,eta,mu) following some laws in category theory * A way of structuring functional programs The first meaning can probably not be described easily in natural language. Michael Arbib and Ernest Manes' "Arrows, Structure, Functors - The Categorical Imperative". describe them as (generalized monoids) in Section 10.2 and through adjointness to the forgetful functor from algebras to sets. That last connection basically makes everything that we can write down or model using abstract syntax / universal algebra a monad. The second view is described in Wadler's papers. I mention category theory because we can describe things that are not computations as monads. It also reminds us why a monad is a collection of things taken together. With the List example in mind, a potentially more revealing account on monads (aka triples) can be found in the free book Barr, Wells
Just fire up your REPL and see for yourself how the malleable syntactic structures of the language grow in front of your eyes, alongside your program. Whether this is through Lisp macros or Ruby meta-programming or Scala control structures, the secret sauce is in the ability to implement more and more powerful abstractions within the language. But what makes one language shine more compared to another is the ability to combine abstractions leading to more powerful syntactic structures. Recently people have been talking about the Maybe monad and its myriads of implementation possibilities in Ruby. Because of its dynamic nature and powerful meta-programming facilities, Ruby allows you to write this .. @phone = Location.find(:first, ...elided... ).andand.phone Here andand is an abstraction of the Maybe monad that you can seamlessly compose with core Ruby syntax structures, effectively growing the Ruby language.