Having used GHC Haskell's software transactional memory features to build a concurrent service with caching, I do think there are significant practical benifits

Having used GHC Haskell's software transactional memory features to build a concurrent service with caching, I do think there are significant practical benifits. To program threaded code without needing to worry about global reasoning of fine-grained locking is a godsend. Transactional memory solves the issue of writing composable code that works on shared mutable state. Task libraries do not solve this problem. Of course retrofitting such a feature into C/C++ in a satisfactory manner might not be possible. But the practical benifits are real.