SetVar C Library man page. Tk embedding Tk embedding now also works on the Macintosh, as long as both the container and embedded application are in the same process. Binary data is handled differently since Tcl 8.1 than in Tcl 8.0. Tcl 8.0 introduced a byte-code compiler for Tcl. The compiler works transparently, automatically compiling code the first time it is executed.
Performance improvements can be large for specific operations, especially list operations.
Execution speed for a whole application is generally about twice as fast as earlier versions of Tcl. TclPro Compiler lets you write out byte-codes and load them directly. This lets you distribute compiled code instead of plain Tcl scripts. Compiler Notes describe effects that the compiler has on Tcl script execution. Tcl automatically manages these values so their type is transparent to the Tcl script writer.