If we introduce for-let, then I think we should have for-reduce for consistency and deprecate the :reduce option. The proposal explains why having it at the beginning allows more possibilities, but other than that they are quite close.
The tuple contract is how it works with map_reduce and that is what we are trying to mirror here. We could try to steer away from it, but then we venture further into unknown territory, which was more generally disliked in previous proposals. The comprehension error won’t catch false positives though, unless we have a type system.
You can re-bind the
letvariables in each iteration, and at the endforscoops up the final values and returns them in a map.
This was actually my first proposal but it was generally disliked. You can see the elixir-lang-core mailing list for more discussion on that. I would link but I am currently on my phone.
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My thoughts on this topic have changed several times but right now I am closer to for_let and for_reduce than for let. The reason is simple: different return types should have different functions.
Makes sense to me.
