Exception-handling languages without this unwinding are Common Lisp with its Condition System, PL/I and Smalltalk. All call the exception handler and do not unwind the stack; however, in PL/I, if the "ON unit" (exception handler) does a GOTO out of the ON unit, that will unwind the stack. The exception handler has the option to restart the computation, resume or unwind. This allows the program to continue the computation at exactly the same place where the error occurred (for example when a previously missing file has become available) or to implement notifications, logging, queries and fluid variables on top of the exception handling mechanism (as done in Smalltalk). The stackless implementation of the "Mythryl" programming language supports constant-time exception handling without stack unwinding.