I think programming languages compose poorly. Monads and effects get nearer to problem we are trying to solve - tying specific behaviour to specific scenarios -

I think programming languages compose poorly. Monads and effects get nearer to problem we are trying to solve - tying specific behaviour to specific scenarios - but impose such as a high threshold of understanding that they are rarely used in practice. If I want to take behaviour you've written and use it in my system I have to do lots of studying your APIs to work out how to represent my solution with your code and API. I am inspired by message passing and Smalltalk but put off by the cache locality of object orientated programming. Making systems that compose is hard work.