One way in which Haskell is potentially less restrictive is the freedom to define your own monads - while some need a degree of compiler or FFI support (IO, ST, STM etc etc), many other useful monads can be built on top of existing language features and provide useful semantics for whichever problem you have at hand. For a couple of domain-specific examples, the Parsec library is good and many type checkers use a monad to provide unification and related services.