If you want them only to "escape" down the stack then it's not necessary. If you want them to escape up the stack then of course you can't have them capture a pointer to the stack variable, because that will no longer exist once the current function returns. However if you capture all variables by value and make the lambda an unique type containing all the captured variables then you can return it up the stack. Of course the downside of this is that each lambda gets its own different type, but you can add ways to convert them to a common type at the cost of having to then deal with the allocation issue at that point.