úÎÞ{ non-portable experimentalmainland@eecs.harvard.edu.Atomically mutate the contents of a reference The 7 type class abstracts over the details of manipulating M references, allowing one to write code that uses references and can operate 2 in any monad that supports reference operations. Create a new reference Read the value of a reference !Write a new value to a reference #Mutate the contents of a reference  ref-fd-0.3.0.1Control.Monad.RefMonadAtomicRefatomicModifyRefMonadRefnewRefreadRefwriteRef modifyRef