This is one reason why I like the old NeXT term "system software" in favor of "OS". (The former is all inclusive.) Blocks are a language feature, and do need

This is one reason why I like the old NeXT term "system software" in favor of "OS". (The former is all inclusive.) Blocks are a language feature, and do need compiler support. The version of the compiler that you need to use them in GCD comes with v10.6 system software.