Which programming languages support constant methods?

Question

Which programming languages other than C++ support the concept of a constant class method? That is, what languages allow the programmer to constrain a method in such a way that it is guaranteed not to change the state of an object to which the method is applied?

Please provide examples or references in your answer.

Answer 1

Haskell, since it's purely functional.

Actually, every value/method is constant in Haskell even though mutable state/IO can be modelled through a mathematical construct called monad.

Answer 2

All purely functional languages are all const by default because purely functional languages have no state to be changed.