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 @settitle The FreeM Manual  @settitle The FreeM Manual
   
 @copying  @copying
 This manual is for FreeM, (version 0.64.0-rc1), which is a free software@footnote{FreeM subscribes to the software licensing philosophy described in @emph{Free Software, Free Society:  This manual is for FreeM, (version 0.64.0-rc1), which is a free software implementation of the M programming language.
 Selected Essays of Richard M. Stallman}.} implementation of the M programming language.  
   
 Print-optimized versions of this book are typeset in @emph{Computer Modern} by the author using the @emph{GNU Texinfo} tools.  Print-optimized versions of this book are typeset in @emph{Computer Modern} by the author using the @emph{GNU Texinfo} tools.
   
Line 699  Please note that FreeM is not entirely s Line 698  Please note that FreeM is not entirely s
 * $SYSTEM::                  MDC system ID of FreeM.  * $SYSTEM::                  MDC system ID of FreeM.
 * $TEST::                    Truth value of last conditional expression or result of certain @code{LOCK} operations.  * $TEST::                    Truth value of last conditional expression or result of certain @code{LOCK} operations.
 * $TLEVEL::                  Current level of transaction nesting.  * $TLEVEL::                  Current level of transaction nesting.
 * $WITH::                    Current variable prefix set by @code{WITH} command.  * $WITH::                    Current variable prefix set by @code{ZWITH} command.
 * $X::                       Current horizontal screen position.  * $X::                       Current horizontal screen position.
 * $Y::                       Current vertical screen position.  * $Y::                       Current vertical screen position.
 * $ZA::                      Current position of file on @code{$IO}.  * $ZA::                      Current position of file on @code{$IO}.
Line 895  uncommitted transactions exist. Line 894  uncommitted transactions exist.
 @cindex $WITH  @cindex $WITH
 @cindex intrinsic special variables, $WITH  @cindex intrinsic special variables, $WITH
   
 Returns the variable prefix set by the @code{@ref{WITH}} command.  Returns the variable prefix set by the @code{@ref{ZWITH}} command.
   
 @node $X  @node $X
 @section $X  @section $X
Line 2018  Identical to @ref{$TRANSLATE()}, except Line 2017  Identical to @ref{$TRANSLATE()}, except
 * AUNBLOCK::                            Decrement the block counter for one or more event classes.  * AUNBLOCK::                            Decrement the block counter for one or more event classes.
 * BREAK::                               Interrupt a running routine to allow interactive debugging.  * BREAK::                               Interrupt a running routine to allow interactive debugging.
 * CLOSE::                               Close an input/output device.  * CLOSE::                               Close an input/output device.
 * CONST::                               Define a constant that cannot be altered after initial definition.  
 * DO::                                  Transfer program control to one or more subroutines or introduces a new execution level.  * DO::                                  Transfer program control to one or more subroutines or introduces a new execution level.
 * ELSE::                                Execute the remainder of a line if @code{@ref{$TEST}} evaluates @emph{false}.  * ELSE::                                Execute the remainder of a line if @code{@ref{$TEST}} evaluates @emph{false}.
 * FOR::                                 Repeat execution of a line or block of code.  * FOR::                                 Repeat execution of a line or block of code.
Line 2031  Identical to @ref{$TRANSLATE()}, except Line 2029  Identical to @ref{$TRANSLATE()}, except
 * KSUBSCRIPTS::                         Kill only the descendant subscripts of a local, global, global, or structured system variable.  * KSUBSCRIPTS::                         Kill only the descendant subscripts of a local, global, global, or structured system variable.
 * KVALUE::                              Kill only the value of a local, global, or structured system variable.  * KVALUE::                              Kill only the value of a local, global, or structured system variable.
 * LOCK::                                Control advisory locking for concurrency control.  * LOCK::                                Control advisory locking for concurrency control.
 * MAP::                                 Map a global name to a non-default namespace.  
 * MERGE::                               Merge contents of one local, global, or structured system variable into another.  * MERGE::                               Merge contents of one local, global, or structured system variable into another.
 * NEW::                                 Introduce a new scope for a specified local variable or intrinsic special variable or instantiate an object.  * NEW::                                 Introduce a new scope for a specified local variable or intrinsic special variable or instantiate an object.
 * OPEN::                                Open a sequential or socket input/output device.  * OPEN::                                Open a sequential or socket input/output device.
Line 2040  Identical to @ref{$TRANSLATE()}, except Line 2037  Identical to @ref{$TRANSLATE()}, except
 * SET::                                 Set the value of a local variable, global, intrinsic special variable, or structured system variable.  * SET::                                 Set the value of a local variable, global, intrinsic special variable, or structured system variable.
 * TCOMMIT::                             Commit a transaction.  * TCOMMIT::                             Commit a transaction.
 * THEN::                                Preserve @code{@ref{$TEST}} until the end of the current line.  * THEN::                                Preserve @code{@ref{$TEST}} until the end of the current line.
 * THROW::                               Programmatically raise an error condition.  
 * TROLLBACK::                           Roll back all pending transactions.  * TROLLBACK::                           Roll back all pending transactions.
 * TSTART::                              Introduce a new transaction processing level.  * TSTART::                              Introduce a new transaction processing level.
 * UNMAP::                               Remove a mapping of a global to a non-default namespace.  
 * USE::                                 Set the currently-active input/output device.  * USE::                                 Set the currently-active input/output device.
 * VIEW::                                Modify FreeM internal parameters.  * VIEW::                                Modify FreeM internal parameters.
 * WATCH::                               Enable or disable watchpoints, or set or clear watchpoints on specified globals, locals, or structured system variables.  
 * WITH::                                Set prefix for future variable references.  
 * WRITE::                               Write output to current input/output device.  * WRITE::                               Write output to current input/output device.
 * XECUTE::                              Interpret string as M code.  * XECUTE::                              Interpret string as M code.
 * ZBREAK::                              Unknown.  * ZBREAK::                              Unknown.
   * ZCONST::                              Define a constant that cannot be altered after initial definition.
 * ZGO::                                 Unknown.  * ZGO::                                 Unknown.
 * ZHALT::                               Unknown.  * ZHALT::                               Unknown.
 * ZINSERT::                             Insert code into routine buffer.  * ZINSERT::                             Insert code into routine buffer.
 * ZJOB::                                Unknown.  * ZJOB::                                Invokes a job, ignoring any timeouts.
 * ZLOAD::                               Load routine into routine buffer.  * ZLOAD::                               Load routine into routine buffer.
   * ZMAP::                                Map a global name to a non-default namespace.
 * ZNEW::                                Unknown.  * ZNEW::                                Unknown.
 * ZPRINT::                              Print contents of routine buffer.  * ZPRINT::                              Print contents of routine buffer.
 * ZQUIT::                               Unknown.  * ZQUIT::                               Quits multiple stack levels at once.
 * ZREMOVE::                             Remove code from routine buffer.  * ZREMOVE::                             Remove code from routine buffer.
 * ZSAVE::                               Save routine buffer to disk.  * ZSAVE::                               Save routine buffer to disk.
   * ZTHROW::                              Programmatically raise an error condition.
 * ZTRAP::                               Unknown.  * ZTRAP::                               Unknown.
   * ZUNMAP::                              Remove a mapping of a global to a non-default namespace.
   * ZWATCH::                              Enable or disable watchpoints, or set or clear watchpoints on specified globals, locals, or structured system variables.
   * ZWITH::                               Set prefix for future variable references.
 * ZWRITE::                              Write local variable, global, or structured system variable to @code{@ref{$IO}}.  * ZWRITE::                              Write local variable, global, or structured system variable to @code{@ref{$IO}}.
 @end menu  @end menu
   
Line 2359  In its argumentless form, @code{CLOSE} c Line 2358  In its argumentless form, @code{CLOSE} c
   
 In its single-argument form, @code{CLOSE} closes the I/O device associated with channel @emph{channel}, provided that @emph{channel} represents a currently-open device, and the optional @emph{postcondition} is @emph{true} or omitted.  In its single-argument form, @code{CLOSE} closes the I/O device associated with channel @emph{channel}, provided that @emph{channel} represents a currently-open device, and the optional @emph{postcondition} is @emph{true} or omitted.
   
 @node CONST  
 @section CONST  
 @cindex CONST  
 @cindex commands, CONST  
 @cindex commands, non-standard  
 @emph{FreeM Extension}  
   
 Defines a local @emph{constant}, or variable that cannot be altered after its initial definition, provided the optional @emph{postcondition} is @emph{true} or omitted.  
   
 Constants must only be locals, and globals are not supported.  
   
 @emph{Syntax}  
   
 @example  
 @code{CONST@emph{:postcondition} @emph{mref1}=@emph{initial-value1},...,@emph{mrefN}=@emph{initial-valueN}}  
 @end example  
   
 @node DO  @node DO
 @section DO  @section DO
 @cindex DO  @cindex DO
Line 2742  If @code{LOCK} succeeds within @emph{tim Line 2724  If @code{LOCK} succeeds within @emph{tim
 LOCK[@emph{:postcondition}] @emph{name}[:@emph{timeout}][,...@emph{name}[:@emph{timeout}]]  LOCK[@emph{:postcondition}] @emph{name}[:@emph{timeout}][,...@emph{name}[:@emph{timeout}]]
 @end example  @end example
   
 @node MAP  
 @section MAP  
 @cindex MAP  
 @cindex commands, MAP  
 @cindex commands, implementation-specific  
 @cindex commands, non-standard  
   
 Maps global name @code{gvn} to be mapped to the non-default namespace @emph{expr V namespace}, provided the optional @emph{postcondition} evaluates to @emph{true} or is omitted.  
   
 @emph{Syntax}  
   
 @example  
 MAP[@emph{:postcondition}] GLOBAL @emph{gvn}=@emph{expr V namespace}  
 @end example  
   
 @node MERGE  @node MERGE
 @section MERGE  @section MERGE
 @cindex MERGE  @cindex MERGE
Line 3006  Saves the value of @code{$TEST} until th Line 2973  Saves the value of @code{$TEST} until th
 IF 1 THEN  WRITE "HELLO!",!  IF 1 THEN  WRITE "HELLO!",!
 @end example  @end example
   
 @node THROW  
 @section THROW  
 @cindex THROW  
 @cindex commands, THROW  
 @cindex commands, non-standard  
 @emph{FreeM Extension}  
   
 Raises an error condition as long as the optional @emph{postcondition} is @emph{true} or omitted.  
   
 @emph{Syntax}  
   
 @example  
 @code{THROW@emph{:postcondition} @emph{expr V error-code}}  
 @end example  
   
 @emph{Example}  
   
 @example  
 @code{THROW "M102"}  
 @end example  
   
 @node TROLLBACK  @node TROLLBACK
 @section TROLLBACK  @section TROLLBACK
 @cindex TROLLBACK  @cindex TROLLBACK
Line 3091  If you are using more than one transacti Line 3037  If you are using more than one transacti
 TSTART (FOO,BAR):(SERIAL,TRANSACTIONID="FOO")  TSTART (FOO,BAR):(SERIAL,TRANSACTIONID="FOO")
 @end example  @end example
   
 @node UNMAP  
 @section UNMAP  
 @cindex UNMAP  
 @cindex commands, UNMAP  
 @cindex commands, implementation-specific  
 @cindex commands, non-standard  
   
 Removes any mapping connecting @emph{gvn} to a non-default namespace, provided the optional @emph{postcondition} evaluates to @emph{true} or is omitted.  
   
 @emph{Syntax}  
   
 @example  
 UNMAP GLOBAL @emph{gvn}  
 @end example  
   
 @node USE  @node USE
 @section USE  @section USE
Line 3409  VIEW 133:@emph{tvexpr} Line 3341  VIEW 133:@emph{tvexpr}
   
 @end table  @end table
   
 @node WATCH  
 @section WATCH  
 @cindex WATCH  
 @cindex commands, WATCH  
 @cindex commands, debugging  
 @cindex commands, implementation-specific  
 @cindex commands, non-standard  
 @emph{FreeM Extension}  
   
 Sets a watchpoint on a global, local, or SSVN node.  
   
 @emph{Syntax}  
   
   
 In its @emph{argumentless} form, @code{WATCH} toggles watchpoints on and off, provided the optional @emph{postcondition} is @emph{true} or omitted.  
   
 @example  
 WATCH[@emph{:postcondition}]  
 @end example  
   
 In its @emph{inclusive} form, @code{WATCH} adds, removes, or examines watchpoints, provided the optional @emph{postcondition} is @emph{true} or omitted.  
   
 A @code{+} adds a new watchpoint to the following variable.  
   
 A @code{-} removes an existing watchpoint for the following variable.  
   
 A @code{?} examines the status of a watchpoint for the following variable.  
   
 @example  
 WATCH[@emph{:postcondition}] [+|-|?]@emph{var1}...,[+|-|?]@emph{varN}  
 @end example  
   
   
 The following example demonstrates turning watchpoint processing on and adding a watchpoint for global variable @code{^snw(1)}. It then changes the value of @code{^snw(1)}.  
   
 @example  
 DEFAULT.USER> WATCH  
    
 Watchpoints enabled.  
    
 DEFAULT.USER> WATCH +^SNW(1)  
    
 Added '^SNW("1")' to the watchlist.  
    
 DEFAULT.USER> SET ^SNW(1)="new value"  
    
 >> WATCHPOINT:  ^SNW("1") => 'new value' (changed 1 times)  
   
 @end example  
   
 The following example will remove that watchpoint:  
   
 @example  
 DEFAULT.USER> WATCH -^SNW(1)  
    
 Removed '^SNW("1")' from the watchlist.  
    
 DEFAULT.USER> WATCH ?^SNW(1)  
    
 '^SNW("1")' is not being watched.  
 @end example  
   
 @node WITH  
 @section WITH  
 @cindex WITH  
 @cindex commands, WITH  
 @cindex commands, non-standard  
 @emph{FreeM Extension}  
   
 NOTE: This command may be deprecated and removed in future FreeM releases.  
   
 Sets a prefix to be applied to all subsequent local variable or constant references.  
   
 @emph{Syntax}  
   
 @example  
 @code{WITH@emph{:postcondition} @emph{var-prefix}}  
 @end example  
   
 In the above single-argument form, sets the @code{$WITH} prefix to @emph{var-prefix}, provided that the optional @emph{postcondition} is either @emph{true} or omitted.  
   
 The @emph{var-prefix} argument may be a string literal or any valid FreeM expression.  
   
 @example  
 @code{WITH@emph{:postcondition}}  
 @end example  
   
 In the above argumentless form, clears the @code{$WITH} prefix, provided the optional @emph{postcondition} is either @emph{true} or omitted. Equivalent to @code{WITH ""}.  
   
   
 @node WRITE  @node WRITE
Line 3518  In the above argumentless form, clears t Line 3362  In the above argumentless form, clears t
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
   @node ZCONST
   @section ZCONST
   @cindex ZCONST
   @cindex commands, ZCONST
   @cindex commands, non-standard
   @emph{FreeM Extension}
   
   Defines a local @emph{constant}, or variable that cannot be altered after its initial definition, provided the optional @emph{postcondition} is @emph{true} or omitted.
   
   Constants must only be locals, and globals are not supported.
   
   @emph{Syntax}
   
   @example
   @code{ZCONST@emph{:postcondition} @emph{mref1}=@emph{initial-value1},...,@emph{mrefN}=@emph{initial-valueN}}
   @end example
   
 @node ZGO  @node ZGO
 @section ZGO  @section ZGO
 @cindex ZGO  @cindex ZGO
Line 3570  Loads routine @emph{<routine-name>} into Line 3431  Loads routine @emph{<routine-name>} into
 ZLOAD@emph{:postcondition} @emph{<routine-name>}  ZLOAD@emph{:postcondition} @emph{<routine-name>}
 @end example  @end example
   
   
   @node ZMAP
   @section ZMAP
   @cindex ZMAP
   @cindex commands, ZMAP
   @cindex commands, implementation-specific
   @cindex commands, non-standard
   
   Maps global name @code{gvn} to be mapped to the non-default namespace @emph{expr V namespace}, provided the optional @emph{postcondition} evaluates to @emph{true} or is omitted.
   
   @emph{Syntax}
   
   @example
   ZMAP[@emph{:postcondition}] GLOBAL @emph{gvn}=@emph{expr V namespace}
   @end example
   
 @node ZNEW  @node ZNEW
 @section ZNEW  @section ZNEW
 @cindex ZNEW  @cindex ZNEW
Line 3628  In its argumentless form, quits from @co Line 3505  In its argumentless form, quits from @co
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
   
   @node ZTHROW
   @section ZTHROW
   @cindex ZTHROW
   @cindex commands, ZTHROW
   @cindex commands, non-standard
   @emph{FreeM Extension}
   
   Raises an error condition as long as the optional @emph{postcondition} is @emph{true} or omitted.
   
   @emph{Syntax}
   
   @example
   @code{ZTHROW@emph{:postcondition} @emph{expr V error-code}}
   @end example
   
   @emph{Example}
   
   @example
   @code{ZTHROW "M102"}
   @end example
   
 @node ZTRAP  @node ZTRAP
 @section ZTRAP  @section ZTRAP
 @cindex ZTRAP  @cindex ZTRAP
Line 3637  In its argumentless form, quits from @co Line 3536  In its argumentless form, quits from @co
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
   @node ZUNMAP
   @section ZUNMAP
   @cindex ZUNMAP
   @cindex commands, ZUNMAP
   @cindex commands, implementation-specific
   @cindex commands, non-standard
   
   Removes any mapping connecting @emph{gvn} to a non-default namespace, provided the optional @emph{postcondition} evaluates to @emph{true} or is omitted.
   
   @emph{Syntax}
   
   @example
   ZUNMAP GLOBAL @emph{gvn}
   @end example
   
   @node ZWATCH
   @section ZWATCH
   @cindex ZWATCH
   @cindex commands, ZWATCH
   @cindex commands, debugging
   @cindex commands, implementation-specific
   @cindex commands, non-standard
   @emph{FreeM Extension}
   
   Sets a watchpoint on a global, local, or SSVN node.
   
   @emph{Syntax}
   
   
   In its @emph{argumentless} form, @code{ZWATCH} toggles watchpoints on and off, provided the optional @emph{postcondition} is @emph{true} or omitted.
   
   @example
   ZWATCH[@emph{:postcondition}]
   @end example
   
   In its @emph{inclusive} form, @code{ZWATCH} adds, removes, or examines watchpoints, provided the optional @emph{postcondition} is @emph{true} or omitted.
   
   A @code{+} adds a new watchpoint to the following variable.
   
   A @code{-} removes an existing watchpoint for the following variable.
   
   A @code{?} examines the status of a watchpoint for the following variable.
   
   @example
   ZWATCH[@emph{:postcondition}] [+|-|?]@emph{var1}...,[+|-|?]@emph{varN}
   @end example
   
   
   The following example demonstrates turning watchpoint processing on and adding a watchpoint for global variable @code{^snw(1)}. It then changes the value of @code{^snw(1)}.
   
   @example
   DEFAULT.USER> ZWATCH
    
   Watchpoints enabled.
    
   DEFAULT.USER> ZWATCH +^SNW(1)
    
   Added '^SNW("1")' to the watchlist.
    
   DEFAULT.USER> SET ^SNW(1)="new value"
    
   >> WATCHPOINT:  ^SNW("1") => 'new value' (changed 1 times)
   
   @end example
   
   The following example will remove that watchpoint:
   
   @example
   DEFAULT.USER> ZWATCH -^SNW(1)
    
   Removed '^SNW("1")' from the watchlist.
    
   DEFAULT.USER> ZWATCH ?^SNW(1)
    
   '^SNW("1")' is not being watched.
   @end example
   
   @node ZWITH
   @section ZWITH
   @cindex ZWITH
   @cindex commands, ZWITH
   @cindex commands, non-standard
   @emph{FreeM Extension}
   
   NOTE: This command may be deprecated and removed in future FreeM releases.
   
   Sets a prefix to be applied to all subsequent local variable or constant references.
   
   @emph{Syntax}
   
   @example
   @code{ZWITH@emph{:postcondition} @emph{var-prefix}}
   @end example
   
   In the above single-argument form, sets the @code{$WITH} prefix to @emph{var-prefix}, provided that the optional @emph{postcondition} is either @emph{true} or omitted.
   
   The @emph{var-prefix} argument may be a string literal or any valid FreeM expression.
   
   @example
   @code{ZWITH@emph{:postcondition}}
   @end example
   
   In the above argumentless form, clears the @code{$WITH} prefix, provided the optional @emph{postcondition} is either @emph{true} or omitted. Equivalent to @code{ZWITH ""}.
   
   
   
   
   
   
   
   
 @node ZWRITE  @node ZWRITE
 @section ZWRITE  @section ZWRITE
 @cindex ZWRITE  @cindex ZWRITE
Line 4579  SET MYSTRING="This is a ""string literal Line 4589  SET MYSTRING="This is a ""string literal
 @cindex types, custom  @cindex types, custom
 @cindex classes  @cindex classes
   
 See @ref{Classes}.  See @ref{Object-Oriented Programming}.
   
 @node Globals  @node Globals
 @chapter Globals  @chapter Globals
Line 4780  The effect of this is that the operation Line 4790  The effect of this is that the operation
 @cindex variables, local  @cindex variables, local
 @cindex local variables  @cindex local variables
   
   @menu
   * Local Variables Overview::            The basics of locals.
   * Creating Local Variables::            Creating locals with SET.
   * Removing Local Variables::            Removing locals with KILL.
   @end menu
   
   @node Local Variables Overview
 @section Local Variables Overview  @section Local Variables Overview
   
 FreeM @emph{local variables} have the same data structure as global variables, but are scoped to a single FreeM process, and stored in memory.  FreeM @emph{local variables} have the same data structure as global variables, but are scoped to a single FreeM process, and stored in memory.
Line 4877  MYRTN ; Line 4894  MYRTN ;
   
 @cartouche  @cartouche
 @quotation  @quotation
 @emph{MDC Type A Extension}  @emph{Style Recommendation}
   
 Note that @code{THEN} is not in any currently published version of the @emph{Standard}, but is part of MDC Type A extension X11/1998-31. However, we recommend using @code{THEN} instead of favoring portability, as there is no defensible reason for this incredibly simple feature @emph{not} to be ubiquitous.  Note that @code{THEN} is not in any currently published version of the @emph{Standard}, but is part of MDC Type A extension X11/1998-31. However, we recommend using @code{THEN} instead of favoring portability, as there is no defensible reason for this incredibly simple feature @emph{not} to be ubiquitous.
   
Line 4928  If you use other M implementations, you Line 4945  If you use other M implementations, you
 @cindex programming, object-oriented  @cindex programming, object-oriented
   
 @menu  @menu
 * Classes::                         The basis of object-oriented programming.  * Classes::                             The organizing concept of object-oriented programming.
 * Inheritance::                     Basing one class upon another.  * Inheritance::                         Making one class derive from another.
 * Methods::                         Attaching code to a class.  * Methods::                             Attach code to classes.
 * Public and Private Variables::    Managing class member access.  * Public and Private Variables::        Determining accessibility.
 * Instantiating Objects::           Creating instances of classes.  * Instantiating Objects::               Creating instances of classes.
 * Determining Object Class::        Getting object information at runtime.  
 @end menu  @end menu
   
 @node Classes  @node Classes
 @section Classes  @section Classes
   
 @menu  
 * Class Overview::                  Class basics.  
 * Constructors::                    Managing object creation.  
 * Destructors::                     Cleaning up.  
 * Runtime Polymorphism::            Selecting methods at runtime.  
 @end menu  
   
 @node Class Overview  
 @subsection Class Overview  @subsection Class Overview
   
 A @emph{class} is the primary organizing concept of FreeM support for object-oriented programming, and in FreeM, is simply an M routine with a few special properties:  A @emph{class} is the primary organizing concept of FreeM support for object-oriented programming, and in FreeM, is simply an M routine with a few special properties:
Line 4964  DESTROY(THIS) ; This is the destructor Line 4971  DESTROY(THIS) ; This is the destructor
   
 The above example demonstrates general class syntax.  The above example demonstrates general class syntax.
   
 @node Constructors  
 @subsection Constructors  @subsection Constructors
   
 A @emph{constructor} is an M entry point that is called when a new instance of a class is created.  A @emph{constructor} is an M entry point that is called when a new instance of a class is created.
Line 4989  A constructor looks like this: Line 4995  A constructor looks like this:
   
 In the above example, @emph{<superclass>} represents the name of a class from which this class should inherit. In this case, the @code{FRACTION} class inherits from the @code{OBJECT} class. Note that this is not strictly necessary in this case, as all classes in FreeM automatically inherit from @code{OBJECT}.  In the above example, @emph{<superclass>} represents the name of a class from which this class should inherit. In this case, the @code{FRACTION} class inherits from the @code{OBJECT} class. Note that this is not strictly necessary in this case, as all classes in FreeM automatically inherit from @code{OBJECT}.
   
 @node Destructors  
 @subsection Destructors  @subsection Destructors
 A @code{destructor} is called when you @code{KILL} an instance variable. Its tag must be @code{DESTROY}, and it must take one argument (@code{THIS}).  A @code{destructor} is called when you @code{KILL} an instance variable. Its tag must be @code{DESTROY}, and it must take one argument (@code{THIS}).
   
Line 5016  Inheritance is achieved by specifying th Line 5021  Inheritance is achieved by specifying th
 CLASS(THIS,INIT):SUPERCLASS  CLASS(THIS,INIT):SUPERCLASS
 @end example  @end example
   
 @node Runtime Polymorphism  
 @subsection Runtime Polymorphism  @subsection Runtime Polymorphism
   
 You can achieve runtime polymorphism by subclassing, and defining methods in the subclass that match the names of existing methods in the superclass. Following FreeM inheritance rules, the overridden method in the subclass will be called, and the method in the superclass will not.  You can achieve runtime polymorphism by subclassing, and defining methods in the subclass that match the names of existing methods in the superclass. Following FreeM inheritance rules, the overridden method in the subclass will be called, and the method in the superclass will not.
Line 5046  DEFAULT.USER> W MYOBJ.MYMETHOD() Line 5050  DEFAULT.USER> W MYOBJ.MYMETHOD()
 VALUE  VALUE
 @end example  @end example
   
 @node Public and Private Variables   @node Public and Private Variables
 @section Public and Private Variables  @section Public and Private Variables
   
 FreeM supports private fields with the @code{:PRIVATE} specifier in the @code{SET} command, enforcing classical object-oriented data encapsulation. The @code{:PUBLIC} specifier is provided for completeness, and is the default.  FreeM supports private fields with the @code{:PRIVATE} specifier in the @code{SET} command, enforcing classical object-oriented data encapsulation. The @code{:PUBLIC} specifier is provided for completeness, and is the default.
Line 5080  NEW MYSTR=$#^%STRING("myString") Line 5084  NEW MYSTR=$#^%STRING("myString")
   
 This will create a local variable called MYSTR of type STRING, and initialize it with the value myString.   This will create a local variable called MYSTR of type STRING, and initialize it with the value myString. 
   
 @node Determining Object Class  @subsection Determining Object Class
 @section Determining Object Class  
   
 To determine the class of any FreeM local variable, you will use the @code{$$TYPE()} method:  To determine the class of any FreeM local variable, you will use the @code{$$TYPE()} method:
   
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