Comment Re:Why is multicore programming so hard? (Score 5, Interesting) 256
Note that I was not talking about automatic parallelization which is indeed possible only with pure languages (and ghc is experimenting on it); but simply about the fact that is is easier to parallelize an application with immutable data structures since you need to care a lot less about synchronization. For instance, the Erlang actors model (also in other languages like Scala on the JVM) still requires the developer to define the tasks to be parallelized, yet immutable data structures make the developer's life a lot easier with respect to concurrent access and usually provide better performance.
My "It is true" was referring to "functional languages" which do usually privilege immutable data structures, not to Haskell or Lisp specifically (which as you said has many variants with mutable structures focused libraries). As you said, Clojure is itself a Lisp-1 and it does privilege immutable data structures and secure concurrent access with Refs/STM or agents. What is more interesting in the Clojure model (compared to Scala's, since they are often compared even though their differences, as functional languages and Java challengers on the JVM) is that it doesn't allow unsafe practices (all must be immutable except in variables local to a thread, etc).
Interesting times on the JVM indeed.