[zodiac]

If you used the State monad for the author's interpreter example, and you did it in Racket (your "state of the world" is a cons-list), what would be the run-time of the resulting interpreter? Similar question for streams (although I'm not that familiar with streams, so I don't know how they would apply here, or if they can be implemented without changes to the base language)

[TuringTest]

A stream is in essence the same as the Observer pattern; every function that depends on the values of a mutable variable must use accessor methods to extract the most recent value when they need it, or pass it 'hook' callback functions that represent the next steps to take on new values.

So, in principle, it should have the same performance as the 'Chil­dren can issue noti­fi­ca­tion events' method in the article, since it's using what in essence is the same structure (just with a much nicer syntax, better adapted to functional programs).

The advantage of using functional streams instead of OOP observable callbacks is that it tends to be easier to write the program's large structure as compositions of functions over streams, i.e. it is easy to build modular functions without the bugs introduced by side effects.

I learned this style of programming through the online 'Paradigms'[1] course by Peter Van Roy, which you can take for free if you don't want credits. It uses the multi-paradigm language Oz to explain the essence of each paradigm and the differences between them. The course distills the primitives of different programming languages in terms of how they see state (see Van Roy's diagram in [2]), and how deciding to incorporate and combine some of those primitives and not others gives rise to the different programming styles. I found it enlightening, in the way that programmers' koans refer to.

[1] https://www.edx.org/es/course/paradigms-of-computer-programm...

[2] https://en.wikipedia.org/wiki/Programming_paradigm#Overview