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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 272  Refers to an M intrinsic special variabl Line 271  Refers to an M intrinsic special variabl
 Indicates a @emph{list} of the following item, e.g., @emph{L gvn} means @emph{list of global variable names}.  Indicates a @emph{list} of the following item, e.g., @emph{L gvn} means @emph{list of global variable names}.
 @item @emph{lvn}  @item @emph{lvn}
 Refers to the name of an M local variable.  Refers to the name of an M local variable.
   @item @emph{postcondition}
   A @emph{tvexpr} immediately following a command verb affecting that command's execution.
 @item @emph{strlit}  @item @emph{strlit}
 Refers to an M string literal.  Refers to an M string literal.
 @item @emph{ssvn}  @item @emph{ssvn}
 Refers to the name of an M structured system variable.  Refers to the name of an M structured system variable.
 @item @emph{tvexpr}  @item @emph{tvexpr}
 Refers to a truth-valued expression.  Refers to a truth-valued expression, i.e., an expression interpreted as a truth value.
 @end table  @end table
   
 @node A Note on Standards  @node A Note on Standards
Line 1712  Returns the Levenshtein distance between Line 1713  Returns the Levenshtein distance between
 @cindex intrinsic functions, $ZM  @cindex intrinsic functions, $ZM
 @cindex intrinsic functions, implementation-specific  @cindex intrinsic functions, implementation-specific
   
   Purpose unknown.
   
 @node $ZNAME()  @node $ZNAME()
 @section $ZNAME  @section $ZNAME
 @cindex $ZNAME  @cindex $ZNAME
Line 2012  Identical to @ref{$TRANSLATE()}, except Line 2015  Identical to @ref{$TRANSLATE()}, except
 * !::                                   Run an external program or command.  * !::                                   Run an external program or command.
 * !!::                                  Launch a subshell from FreeM direct mode.  * !!::                                  Launch a subshell from FreeM direct mode.
 * ABLOCK::                              Increment the block counter for one or more event classes.  * ABLOCK::                              Increment the block counter for one or more event classes.
 * ASSERT::                              Raise error when a conditional expression evaluates @emph{false}.  
 * ASTART::                              Enable asynchronous event handling for one or more event classes.  * ASTART::                              Enable asynchronous event handling for one or more event classes.
 * ASTOP::                               Disable asynchronous event handling for one or more event classes.  * ASTOP::                               Disable asynchronous event handling for one or more event classes.
 * AUNBLOCK::                            Decrement the block counter for one or more event classes.  * AUNBLOCK::                            Decrement the block counter for one or more event classes.
Line 2044  Identical to @ref{$TRANSLATE()}, except Line 2046  Identical to @ref{$TRANSLATE()}, except
 * VIEW::                                Modify FreeM internal parameters.  * VIEW::                                Modify FreeM internal parameters.
 * 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.  * ZASSERT::                             Raise error when a conditional expression evaluates @emph{false}.
   * ZBREAK::                              Enable/disable ZBREAK mode.
 * ZCONST::                              Define a constant that cannot be altered after initial definition.  * ZCONST::                              Define a constant that cannot be altered after initial definition.
 * ZGO::                                 Unknown.  * ZGOTO::                               @code{GOTO} with @code{BREAK} control.
 * ZHALT::                               Unknown.  * ZHALT::                               Exit FreeM job with return value.
 * ZINSERT::                             Insert code into routine buffer.  * ZINSERT::                             Insert code into routine buffer.
 * ZJOB::                                Invokes a job, ignoring any timeouts.  * ZJOB::                                Invoke 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.  * 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::                               Quits multiple stack levels at once.  * ZQUIT::                               Quit 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.  * ZTHROW::                              Programmatically raise an error condition.
 * ZTRAP::                               Unknown.  * ZTRAP::                               Raise a FreeM error.
 * ZUNMAP::                              Remove a mapping of a global to a non-default namespace.  * 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.  * 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.  * ZWITH::                               Set prefix for future variable references.
Line 2183  In its inclusive form, @code{ABLOCK} inc Line 2186  In its inclusive form, @code{ABLOCK} inc
   
 In its exclusive form, @code{ABLOCK} increments the block counters for all event classes @emph{except for} those named in the list, provided the optional @emph{postcondition} is either @emph{true} or omitted.  In its exclusive form, @code{ABLOCK} increments the block counters for all event classes @emph{except for} those named in the list, provided the optional @emph{postcondition} is either @emph{true} or omitted.
   
 @node ASSERT  
 @section ASSERT  
 @cindex ASSERT  
 @cindex commands, ASSERT  
 @cindex commands, debugging  
 @cindex commands, implementation-specific  
 @cindex commands, non-standard  
 @emph{FreeM Extension}  
   
 Triggers error @code{ASSERT} if the supplied truth-valued expression @emph{tvexpr} is @emph{false} (@emph{1} is @emph{true}, and @emph{0} is @emph{false}), and that the optional @emph{postcondition} evaluates to @emph{true} or is omitted.  
   
 The @code{ASSERT} error is catchable whether using standard-style, FreeM-style, or DSM 2.0-style error processing.  
   
 @emph{Syntax}  
   
 @example  
  ASSERT@emph{:postcondition} @emph{<tvexpr>}  
 @end example  
   
 @emph{Example}  
   
 @example  
 DEFAULT.USER> SET DEBUG=1  
   
   
 DEFAULT.USER> ASSERT:DEBUG 1=1  
   
   
 DEFAULT.USER> ASSERT:DEBUG 1=0  
    
    
 >> Error ZASSERT:  programmer assertion failed in SYSTEM::^%SYSINIT  [$STACK = 0]  
 >> ASSERT:DEBUG 1=0  
                    ^  
 @end example  
   
 @node ASTART  @node ASTART
 @section ASTART  @section ASTART
Line 3354  VIEW 133:@emph{tvexpr} Line 3322  VIEW 133:@emph{tvexpr}
 @cindex XECUTE  @cindex XECUTE
 @cindex commands, XECUTE  @cindex commands, XECUTE
   
   @node ZASSERT
   @section ZASSERT
   @cindex ZASSERT
   @cindex commands, ZASSERT
   @cindex commands, debugging
   @cindex commands, implementation-specific
   @cindex commands, non-standard
   @emph{FreeM Extension}
   
   Triggers error @code{ZASSERT} if the supplied truth-valued expression @emph{tvexpr} is @emph{false} (@emph{1} is @emph{true}, and @emph{0} is @emph{false}), and that the optional @emph{postcondition} evaluates to @emph{true} or is omitted.
   
   The @code{ZASSERT} error is catchable whether using standard-style, FreeM-style, or DSM 2.0-style error processing.
   
   @emph{Syntax}
   
   @example
    ZASSERT@emph{:postcondition} @emph{<tvexpr>}
   @end example
   
   @emph{Example}
   
   @example
   DEFAULT.USER> SET DEBUG=1
   
   
   DEFAULT.USER> ZASSERT:DEBUG 1=1
   
   
   DEFAULT.USER> ZASSERT:DEBUG 1=0
    
    
   >> Error ZASSERT:  programmer assertion failed in SYSTEM::^%SYSINIT  [$STACK = 0]
   >> ZASSERT:DEBUG 1=0
                      ^
   @end example
   
 @node ZBREAK  @node ZBREAK
 @section ZBREAK  @section ZBREAK
 @cindex ZBREAK  @cindex ZBREAK
Line 3363  VIEW 133:@emph{tvexpr} Line 3367  VIEW 133:@emph{tvexpr}
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
   Sets or clears the @code{ZBREAK} flag@footnote{NOTE: FreeM team needs to investigate how @code{zbreakon} and @code{zbflag} affect program execution.}, based on the result of evaluating @emph{tvexpr}.
   
   @emph{Syntax}
   
   @example
   ZBREAK @emph{tvexpr}
   @end example
   
 @node ZCONST  @node ZCONST
 @section ZCONST  @section ZCONST
 @cindex ZCONST  @cindex ZCONST
Line 3380  Constants must only be locals, and globa Line 3392  Constants must only be locals, and globa
 @code{ZCONST@emph{:postcondition} @emph{mref1}=@emph{initial-value1},...,@emph{mrefN}=@emph{initial-valueN}}  @code{ZCONST@emph{:postcondition} @emph{mref1}=@emph{initial-value1},...,@emph{mrefN}=@emph{initial-valueN}}
 @end example  @end example
   
 @node ZGO  @node ZGOTO
 @section ZGO  @section ZGOTO
 @cindex ZGO  @cindex ZGOTO
 @cindex commands, ZGO  @cindex commands, ZGOTO
 @cindex commands, implementation-specific  @cindex commands, implementation-specific
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
   In its argumented form, enables @code{BREAK} mode and branches unconditionally to @emph{entryref}.
   
   @emph{Syntax}
   
   @example
   ZGOTO @emph{entryref}
   @end example
   
   In its argumented form, resumes execution after a @code{BREAK}.
   
   @emph{Syntax}
   
   @example
   ZGOTO
   @end example
   
 @node ZHALT  @node ZHALT
 @section ZHALT  @section ZHALT
 @cindex ZHALT  @cindex ZHALT
Line 3396  Constants must only be locals, and globa Line 3424  Constants must only be locals, and globa
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
   In its single-argumented form, @code{ZHALT} command is used to exit the FreeM process with a specific return value @emph{intexpr}.
   
   @emph{Syntax}
   
   @example
   ZHALT @emph{intexpr}
   @end example
   
   In its argumentless form, @code{ZHALT} is synonymous with @code{HALT}.
   
   @emph{Syntax}
   
   @example
   ZHALT
   @end example
   
 @node ZINSERT  @node ZINSERT
 @section ZINSERT  @section ZINSERT
 @cindex ZINSERT  @cindex ZINSERT
Line 3537  Raises an error condition as long as the Line 3581  Raises an error condition as long as the
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
   Synonymous with @ref{ZTHROW}.
   
 @node ZUNMAP  @node ZUNMAP
 @section ZUNMAP  @section ZUNMAP
 @cindex ZUNMAP  @cindex ZUNMAP
Line 4590  SET MYSTRING="This is a ""string literal Line 4636  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 4946  If you use other M implementations, you Line 4992  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
   
   
 @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 4976  DESTROY(THIS) ; This is the destructor Line 5018  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 5001  A constructor looks like this: Line 5042  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 5028  Inheritance is achieved by specifying th Line 5068  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 5058  DEFAULT.USER> W MYOBJ.MYMETHOD() Line 5097  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 5092  NEW MYSTR=$#^%STRING("myString") Line 5131  NEW MYSTR=$#^%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:
   
Line 5690  Raised when you attempt to use multiple Line 5728  Raised when you attempt to use multiple
 Raised when attempts are made to set @code{$ECODE} to an invalid error code value. Obsolete and replaced by standard error code @code{M101}.  Raised when attempts are made to set @code{$ECODE} to an invalid error code value. Obsolete and replaced by standard error code @code{M101}.
   
 @item @code{ZASSERT} - @emph{programmer assertion failed}  @item @code{ZASSERT} - @emph{programmer assertion failed}
 Raised when an @code{ASSERT} expression's result is not true.  Raised when an @code{ZASSERT} expression's result is not true.
   
 @item @code{ZUSERERR} - @emph{user-defined error}  @item @code{ZUSERERR} - @emph{user-defined error}
 Raised when program code calls @code{THROW} with an error code argument for which the first character is @code{U}, or when @code{$ECODE} is set to an error code for which the first character is @code{U}.  Raised when program code calls @code{THROW} with an error code argument for which the first character is @code{U}, or when @code{$ECODE} is set to an error code for which the first character is @code{U}.
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  Added in v.1.51

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