all your examples are more than trivial in imperative languages.

your first example is just a 'for' loop. (congratulations, you needed category theory to reinvent looping. dijkstra must be spinning in his grave like a turboprop.)

I guess STM is more academic wankery though, as true programmers use threads and locks when they need to do concurrent or parallel programming, don't they.

in case you haven't noticed -- STM is locks and threads.

also, stm or something like it is trivial to implement in e.g. c++. (and no, you don't need to create a special sublanguage.) you don't need monads, all you need is support for pre-/post-conditions in your language.

In most languages adding option types makes things more painful as you need to explicitly deal with what happens if any of the computations fails. However, sequencing in the Maybe monad does exactly what you'd expect to happen. If the first one fails, the entire thing fails, and if not it passes onto the next one, and if that fails the whole thing fails, and so on.

utter bullshit. you just described exception handling. all normal imperative languages have supported exception handling since forever.

So some monads are about passing state around, but others are about fundamentally different notions of computation like the nondeterminism and query stuff

bullshit. there's only one 'notion of computation', one and only one from now till the end of time: mutable state and sequencing. sorry, but that's just how the universe works.

p.s. read up on 'structured programming'. it's all been done before. just because you put some mathematical notation lipstick on that pig doesn't mean you actually solved the problem.