What is the mutator?

[Malcolm Wallace]

> i'm not an expert, but:  once value of thunk is evaluated, it's  
> written
> back by code called mutator

Whilst that is indeed mutation, it is not what is usually referred to  
as the "mutator" in the context of garbage collection.  Quite simply,  
the "mutator" is the actual running program, as opposed to the GC,  
which is part of the underlying runtime system.  Conceptually, the  
mutator and GC are the two mutually-exclusive threads of control that  
modify the heap.  Usually one must halt while the other runs.

Regards,
     Malcolm