names if they don't have them already, and the names are assigned
at the return site.

	  func foo() (#rv1 A, #rv2 B) {

		{
			var (
				#next int
			)
			f(func(x T1) bool {
				...
				{
					// return a, b
					#rv1, #rv2 = a, b
					#next = -1
					return false
				}
				...
				return true
			})
			if #next == -1 { return }
		}