On Tue, May 20, 2014 at 11:01 AM, silvio
We could call it (<- exp) instead of ({ exp }) if that makes everyone feel more confortable but I don't see a reason to restrict it to if and case. It can could go into any expression.
This extension has been proposed a number of times. Also there are haskell-like languages that implement it, e.g. using !expr. Looks like at least Idris does, maybe also elm or habit or whatever else. I can't find the write up on the haskell wiki for (<- expr), but I think the sticking point was how the desugaring should happen in nested expressions, and ambiguity about which level the (>>=) should happen at. That said, Idris apparently wasn't bothered by this. So perhaps the way forward is to find the old proposal (or make a new one, if it's gone), and see if Idris's solution applies to haskell.