Eric Elliott

Join means different things for different monads.

“…we can use use join to get our M b on which we can then further call chain/bind or map/fmap. This will not work if flatten/join is ever allowed to return something that is not of the M monad type.”

If you have some code that is not working, please share it so we can spot the real issue. composeM() works, as far as I know.

To get a better handle on what’s happening in .reduce() when you omit an initial value, try the following:

[1, 2, 3].reduce((a, b) => (
  console.log(`a: ${ a }, b: ${ b }`) …

I have no vested interest in whether or not TDD is effective. I use and teach whatever works (and TDD does). If a convincing meta-study came out tomorrow recommending a better practice, I’d investigate and if it works, recommend that instead. Everything else would be business as usual.