úÎË>Class connecting mutable variables and monads they exists in. portablenone:Class connecting mutable variable and monad it exists in. Create new reference. An initial value Reads a reference.  Reference Write to reference.  Reference  New value EModify the reference. Default implementation is provided but it MUST F be overloaded if the reference is atomic to provide an atomic write.  Reference  Computation Result of computation  reference-0.1Data.Reference ReferencenewRefreadRefwriteRef modifyRef