[TODO after the rehearsal talk: add links to code files]
Generators are re-entering functions; meaning that execution can be resumed after returning a value. This gives you the possibility to write any sequence of values in a very declarative fashion.
To do this, you usually need an infinite loop and each time you compute an element of your sequence, you « return » it to the caller. Once the generator is called again, execution can be resumed at the same location it originally halted; giving you the opportunity to compute the next element of the sequence and so on.
Two remarks about the behaviour of the yield keyword open new doors to how we can use(misuse 🤔?) generators.
- First of all
yield ...;is an expression and its value is given by whatever code calls.next()on the generator. - Also up the the generator’s caller,
yield ...;can behave as areturninstruction or athrow.
We can for example fully simulate async/await using Promises and yield or even cooperative threads to name a few.
Redux-saga is an example of a runtime implementing many coding patterns that take advantage of yield. When combined with a redux store, you obtain an easy way of manipulating the program’s state without actually running the side effects.