If you're designing a programming language, and you're planning to include monads solely for the sake of IO, the author has a point: Monads are a very complex w

If you're designing a programming language, and you're planning to include monads solely for the sake of IO, the author has a point: Monads are a very complex way to perform IO, and you're better off with a simpler abstraction. But monads are good for dozens of other things, including Bayesian inference[1], computation with optional values, list comprehensions, software transactional memory, quantum mechanics[2] and (to geek out a bit) anything that involves defining a lambda-calculus analog over a topos. Any time your problem domain includes a bunch of hairy matrix math, there may be a lovely, intuitive formulation using monads. Now, if you're never programmed in Haskell, or if you've stuck to the IO monad, you may not understand why monads are a powerful way to tackle certain kinds of problems. But if you've never used monads in anger, how do you whether or not they're a useful tool? If you want a relatively programmer-friendly language that supports monads, check out Scala's 'for' loop. It looks like a list comprehension, but it gives you about 90% of what you want from monads in practice. [1] Here's an article I wrote on probabilistic programming with monads: http://www.randomhacks.net/articles/2007/02/22/bayes-rule-and-drug-tests http://www.randomhacks.net/articles/2007/02/22/bayes-rule-an... [2] Here's a much cooler article on quantum mechanics with monads: http://blog.sigfpe.com/2007/03/monads-vector-spaces-and-quantum.html http://blog.sigfpe.com/2007/03/monads-vector-spaces-and-quan...