I remember Martin Odersky explaining how the Scala compiler has to do a lot of work to compile FP code to a JVM that is mostly geared for the Java language only. 
Because of that the compiler is well positioned to compile to other targets as well. Like Javascript or LLVM.<p>Are you talking about compromises in the language or the standard library?
In the language itself I can only think of type erasure for generics having to follow the JVM choice.