What does parallelReduce do?

[TheChronicMonster]

parallelReduce is an abbreviation of a while loop combined with a fork.

parallelReduce allows a value to be repeatedly updated by racing participants until the while loop's condition is no longer true.

https://docs.reach.sh/rsh/consensus/#parallelreduce--intuition

[hmzdot]

parallelReduce name comes from the fact that participants are trying to produce a new state from the current values in parallel. So while Alice is producing a new state, Bob might also be producing one. Parallel reduce is essentially a fork+case loop and what this really means is Reach first determines who tried to update the state first (fork) and depending on the winner of the race runs a specified logic (case)
So it's like reduce function in JavaScript but for multiple threads. In our case threads are different participants running the program

Note: In case you didn't know, reduction means taking a bunch of items and processing them recursively, so that result of the previous process become the input of the next one. As an example, if we were to reduce [1, 2, 3] list with const add = (previous, next) => previous + next function with starting value of 0, steps would be:

• prev: 0, next: 1, add(prev, next): 1
• prev: 1, next: 2, add(prev, next): 3
• prev: 3, next: 3, add(prev, next): 6