Well written compilers for functional programming language do not copy immutable data. I recommend searching for “Immutable Data Structures” to see how you can

Well written compilers for functional programming language do not copy immutable data. I recommend searching for “Immutable Data Structures” to see how you can implement very high performance immutable data structures. Haskell and Closure (for example) does this and Haskell is faster than most imperative languages out there. I recommend learning more about this subject.