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Line 4 Line 4
 @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 0.65.1-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.
   
 Copyright @copyright{} 2014-2025 Coherent Logic Development LLC  Copyright @copyright{} 2014-2025 Coherent Logic Development LLC
   
Line 19  Permission is granted to copy, distribut Line 19  Permission is granted to copy, distribut
   
 @title The FreeM Manual  @title The FreeM Manual
 @subtitle @sc{The Official Manual of FreeM}  @subtitle @sc{The Official Manual of FreeM}
 @subtitle Version 0.64.0-rc1  @subtitle Version 0.65.1-rc1
 @c@vskip 10pt  @c@vskip 10pt
 @c@center @image{freem-logo-sm,,,,.png}  @c@center @image{freem-logo-sm,,,,.png}
 @author Serena Willis  @author Serena Willis
Line 44  This is the official manual for the Free Line 44  This is the official manual for the Free
 @menu  @menu
 * Introduction::                        About the FreeM Project, its history, and its goals.  * Introduction::                        About the FreeM Project, its history, and its goals.
 * Document Conventions::                Conventions used in this manual.  * Document Conventions::                Conventions used in this manual.
   * A Note on Standards::                 FreeM positioning regarding the M Development Committee.
 * FreeM Invocation::                    How to invoke FreeM from the command line.  * FreeM Invocation::                    How to invoke FreeM from the command line.
 * The FreeM Environment Daemon::        Managing shared resources in the FreeM environment.  * The FreeM Environment Daemon::        Managing shared resources in the FreeM environment.
 * The FreeM Direct-Mode Environment::   Executing M programs interactively.  * The FreeM Direct-Mode Environment::   Executing M programs interactively.
 * Debugging::                           The program development cycle of FreeM.  * Debugging::                           The program development cycle of FreeM.
   * Program Development Cycle::           How to create, edit, test, and run FreeM programs.
   
 * Directives::                          Per-Routine Language Directives.  * Directives::                          Per-Routine Language Directives.
 * Intrinsic Special Variables::         Intrinsic Special Variables.  * Intrinsic Special Variables::         Intrinsic Special Variables.
Line 99  This is the official manual for the Free Line 101  This is the official manual for the Free
 * Accessing FreeM from C Programs::     How to use the mlib interface.  * Accessing FreeM from C Programs::     How to use the mlib interface.
   
 * FreeM Administrator::                 The fmadm system manager tool.  * FreeM Administrator::                 The fmadm system manager tool.
 * FreeM Legacy Utilities::              FreeM legacy system manager utilities.  
 * FreeM VIEW Commands and Functions::   Getting and setting info about FreeM internals.  * FreeM VIEW Commands and Functions::   Getting and setting info about FreeM internals.
 * Implementation Limits::               FreeM limitations.  * Implementation Limits::               FreeM limitations.
 * US-ASCII Character Set::              The US-ASCII character set.  * US-ASCII Character Set::              The US-ASCII character set.
Line 117  When GT.M was open-sourced in late 1999, Line 118  When GT.M was open-sourced in late 1999,
   
 In February of 2020, work began in earnest to build a development and support infrastructure for FreeM and begin the careful process of refining it into a more stable and robust application.  In February of 2020, work began in earnest to build a development and support infrastructure for FreeM and begin the careful process of refining it into a more stable and robust application.
   
   For more information on FreeM history, see @code{@emph{$PREFIX}/share/freem/doc/freem_history.*} (distributed in PostScript, PDF, and plain text formats).
   
 @section Production Readiness  @section Production Readiness
   
 FreeM is not yet production-ready. There are several show-stopping bugs that preclude a general release for public use:  FreeM is not yet production-ready. There are several show-stopping bugs that preclude a general release for public use:
Line 146  Current contributors denoted with a @emp Line 149  Current contributors denoted with a @emp
 @cindex contributors, Gerum, Winfried  @cindex contributors, Gerum, Winfried
 @cindex contributors, Kreis, Greg  @cindex contributors, Kreis, Greg
 @cindex contributors, Landis, Larry  @cindex contributors, Landis, Larry
   @cindex contributors, McGlothlen, Ken
 @cindex contributors, Milligan, Lloyd  @cindex contributors, Milligan, Lloyd
 @cindex contributors, Morris, Steve  @cindex contributors, Morris, Steve
 @cindex contributors, Murray, John  @cindex contributors, Murray, John
Line 187  Larry Landis (Coordination, Code, Docume Line 191  Larry Landis (Coordination, Code, Docume
 Rick Marshall (Testing, MDC Conformance) @emph{+}  Rick Marshall (Testing, MDC Conformance) @emph{+}
   
 @item  @item
   Ken McGlothlen (Apple Silicon build/test environment, proofreading of documentation) @emph{+}
   
   @item
 Lloyd Milligan (Code, Testing, Documentation)  Lloyd Milligan (Code, Testing, Documentation)
   
 @item  @item
Line 248  FreeM uses abbreviations for common lang Line 255  FreeM uses abbreviations for common lang
 @table @asis  @table @asis
 @item @emph{$PREFIX}  @item @emph{$PREFIX}
 Refers to the base filesystem location within which FreeM is installed. For most distribution methods of FreeM, @emph{$PREFIX} represents either @code{/} or @code{/usr/local}.  Refers to the base filesystem location within which FreeM is installed. For most distribution methods of FreeM, @emph{$PREFIX} represents either @code{/} or @code{/usr/local}.
   @item @emph{dlabel}
   Refers to a label in an M routine, beginning in the first column of the line. Can be a @emph{name} or an @emph{intlit}.
   @item @emph{entryref}
   Refers to an M routine entry point, denoted in the format @code{@emph{dlabel} [+@emph{intexpr}][^@emph{routine}]}.
 @item @emph{expr}  @item @emph{expr}
 Refers to any expression. Often presented in the format @emph{expr V <type>}, where @emph{V} means @emph{giving}; e.g., @emph{expr V lvn} means @emph{expression giving local variable name}.  Refers to any expression. Often presented in the format @emph{expr V <type>}, where @emph{V} means @emph{giving}; e.g., @emph{expr V lvn} means @emph{expression giving local variable name}.
 @item @emph{glvn}  @item @emph{glvn}
Line 256  Refers to the name of an M global, local Line 267  Refers to the name of an M global, local
 Refers to the name of an M global variable.  Refers to the name of an M global variable.
 @item @emph{intexpr}  @item @emph{intexpr}
 Refers to an integer expression.  Refers to an integer expression.
   @item @emph{intlit}
   Refers to an integer literal.
 @item @emph{ISV}, @emph{isv}  @item @emph{ISV}, @emph{isv}
 Refers to an M intrinsic special variable; @code{$JOB} and @code{$IO} are examples of ISVs.  Refers to an M intrinsic special variable; @code{$JOB} and @code{$IO} are examples of ISVs.
 @item @emph{L}  @item @emph{L}
 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}
   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
   @chapter A Note on Standards
   @cindex MDC
   @cindex M Development Committee
   @cindex ANSI X11.1
   @cindex standards, ANSI
   @cindex standards, MDC
   
   FreeM attempts to implement as many features as possible from the M Development Committee's unpublished @emph{Millennium Draft Standard}, as well as its predecessors.
   
   The maintainer of FreeM (who is also the author of this book) is largely in favor of standardization efforts, and hopes that the MDC will resume activities, and will happily participate if it does so in an open, public, transparent, and democratic manner. Until then, however, FreeM will attempt to improve the M language, in cooperation with other free software M implementers where possible. Any breaking changes introduced in future MDC releases of the @emph{Standard} (such as the rumored @emph{M5}) which prove incompatible with FreeM will be handled via the @code{$DIALECT} special variable (to be changed to @code{$ZDIALECT} in a coming release).
   
   The conformance document required per the @emph{Standard} should be installed as a @code{man} page on any computer system where FreeM is made available. Simply type @code{man freem_conformance} to access.
   
 @node FreeM Invocation  @node FreeM Invocation
 @chapter FreeM Invocation  @chapter FreeM Invocation
 @cindex invocation, command-line  @cindex invocation, command-line
Line 399  If the daemon is started with @option{-- Line 430  If the daemon is started with @option{--
   
 The @option{--environment} option will start the daemon for the specified @emph{environment-name}. The default environment, if unspecified, is called @code{DEFAULT}. If using an environment other than @code{DEFAULT}, interpreter processes that wish to also connect to the same environment must also use the @option{--environment} option when starting, and @code{libfreem} clients must also pass the environment name as the first argument to the @code{freem_init()} function. Environments allow you to run multiple, isolated instances of FreeM on the same machine, whose globals and routines are distinct and unique.  The @option{--environment} option will start the daemon for the specified @emph{environment-name}. The default environment, if unspecified, is called @code{DEFAULT}. If using an environment other than @code{DEFAULT}, interpreter processes that wish to also connect to the same environment must also use the @option{--environment} option when starting, and @code{libfreem} clients must also pass the environment name as the first argument to the @code{freem_init()} function. Environments allow you to run multiple, isolated instances of FreeM on the same machine, whose globals and routines are distinct and unique.
   
 The @option{--shmsize} option specifies the size in bytes of the FreeM shared memory segment. The default is 4194304 bytes. Increasing the size of the FreeM shared memory segment will, at the cost of increased memory usage, increase the number of concurrent jobs and lock table entries available to the environment; decreasing the size of the segment will have the expected opposite effect. Note that you must also pass @option{--shmsize} with the same number of bytes to any interpreter process to be used with an environment whose daemon uses a non-default shared memory segment size.  The @option{--shmsize} option specifies the size in bytes of the FreeM shared memory segment. The default is 16,777,216 bytes (16 megabytes). Increasing the size of the FreeM shared memory segment will, at the cost of increased memory usage, increase the number of concurrent jobs and lock table entries available to the environment; decreasing the size of the segment will have the expected opposite effect. Note that you must also pass @option{--shmsize} with the same number of bytes to any interpreter process to be used with an environment whose daemon uses a non-default shared memory segment size.
   
 Attempting to start a FreeM interpreter process without a daemon running with the same environment name will result in an error.  Attempting to start a FreeM interpreter process without a daemon running with the same environment name will result in an error.
   
Line 414  Attempting to start a FreeM interpreter Line 445  Attempting to start a FreeM interpreter
 The FreeM direct-mode environment is the mode entered when FreeM is invoked without the use of @option{-r @emph{<entryref>}} or @option{--routine=@emph{<entryref>}}:  The FreeM direct-mode environment is the mode entered when FreeM is invoked without the use of @option{-r @emph{<entryref>}} or @option{--routine=@emph{<entryref>}}:
   
 @example  @example
 Coherent Logic Development FreeM version 0.64.0-rc1 (x86_64-pc-linux-gnu)  Coherent Logic Development FreeM version 0.65.1-rc1 (x86_64-pc-linux-gnu)
 Copyright (C) 2014, 2020, 2021 Coherent Logic Development LLC  Copyright (C) 2014, 2020, 2021 Coherent Logic Development LLC
   
   
Line 576  FreeM includes an interactive debugger, Line 607  FreeM includes an interactive debugger,
 If you would like to enter the debugger automatically each time an error is encountered, add the following to your @code{LCLINIT} routine:  If you would like to enter the debugger automatically each time an error is encountered, add the following to your @code{LCLINIT} routine:
   
 @example  @example
 S $ETR="B ""DEBUG"""  S $ETRAP="B ""DEBUG"""
 @end example  @end example
   
 @section Debugging Commands  @section Debugging Commands
Line 603  Halts the process being debugged and ret Line 634  Halts the process being debugged and ret
 With no arguments, toggles watchpoints on and off. With @code{+}, adds @emph{<glvn>} to the watchlist. With @code{-}, removes @emph{<glvn>} from the watchlist. With @code{?}, queries the watch status of @emph{<glvn>}.  With no arguments, toggles watchpoints on and off. With @code{+}, adds @emph{<glvn>} to the watchlist. With @code{-}, removes @emph{<glvn>} from the watchlist. With @code{?}, queries the watch status of @emph{<glvn>}.
 @end table  @end table
   
   @node Program Development Cycle
   @chapter Program Development Cycle
   @cindex program development
   
   This chapter covers the essential activities of program development in the FreeM environment, including viewing, creating, editing, and running routines.
   
 @node Directives  @node Directives
 @chapter Directives  @chapter Directives
 @cindex directives  @cindex directives
Line 673  Please note that FreeM is not entirely s Line 710  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 869  uncommitted transactions exist. Line 906  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 1088  See @emph{https://wiki.osdev.org/Target_ Line 1125  See @emph{https://wiki.osdev.org/Target_
 * $ZLSD()::                             Compute Levenshtein distance between two arguments.  * $ZLSD()::                             Compute Levenshtein distance between two arguments.
 * $ZM()::                               Unknown.  * $ZM()::                               Unknown.
 * $ZNAME()::                            Unknown.  * $ZNAME()::                            Unknown.
 * $ZNEXT()::                            Unknown.  * $ZNEXT()::                            Return glvn of next numeric subscript following given glvn.
 * $ZORDER()::                           Unknown.  * $ZORDER()::                           Unknown.
 * $ZPIECE()::                           Unknown.  * $ZPIECE()::                           Unknown.
 * $ZPREVIOUS()::                        Unknown.  * $ZPREVIOUS()::                        Unknown.
Line 1286  The optional second argument indicates t Line 1323  The optional second argument indicates t
 @cindex intrinsic functions, $NEXT  @cindex intrinsic functions, $NEXT
   
 Deprecated. Use @code{$ORDER} instead.  Deprecated. Use @code{$ORDER} instead.
   Returns the next numeric subscript of the specified glvn.
   
   @emph{Syntax}
   
   @example
   $NEXT(@emph{glvn})
   @end example
   
   @emph{Example}
   
   Assume the following array:
   
   @example
   ^foo(1)=""
   ^foo(2)=""
   @end example
   
   And the following code:
   
   @example
    W $ZNEXT(^foo(1)) ; => 2
   @end example 
   
 @node $ORDER()  @node $ORDER()
 @section $ORDER  @section $ORDER
Line 1686  Returns the Levenshtein distance between Line 1745  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 1694  Returns the Levenshtein distance between Line 1755  Returns the Levenshtein distance between
   
 Purpose unknown.  Purpose unknown.
   
   This function relies on the value of @code{$VIEW(71)} being @code{0} (this is not the default).
   
 @node $ZNEXT()  @node $ZNEXT()
 @section $ZNEXT  @section $ZNEXT
 @cindex $ZNEXT  @cindex $ZNEXT
 @cindex intrinsic functions, $ZNEXT  @cindex intrinsic functions, $ZNEXT
 @cindex intrinsic functions, implementation-specific  @cindex intrinsic functions, implementation-specific
   
 Purpose unknown.  Returns a fully-formed variable reference of the next numeric subscript of the specified glvn.
   
   @emph{Syntax}
   
   @example
   $ZNEXT(@emph{glvn})
   @end example
   
   @emph{Example}
   
   Assume the following array:
   
   @example
   ^foo(1)=""
   ^foo(2)=""
   @end example
   
   And the following code:
   
   @example
    W $ZNEXT(^foo(1)) ; => ^foo(2)
   @end example
   
   This function relies on the value of @code{$VIEW(71)} being @code{1} (this is the default).
   
 @node $ZORDER()  @node $ZORDER()
 @section $ZORDER  @section $ZORDER
Line 1986  Identical to @ref{$TRANSLATE()}, except Line 2072  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.
 * 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{$TEST}} evaluates @emph{false}.
 * FOR::                                 Repeat execution of a line or block of code.  * FOR::                                 Repeat execution of a line or block of code.
Line 2005  Identical to @ref{$TRANSLATE()}, except Line 2089  Identical to @ref{$TRANSLATE()}, except
 * KSUBSCRIPTS::                         Kill only the descendant subscripts of a local, global, global, or structured system variable.  * KSUBSCRIPTS::                         Kill only the descendant subscripts of a local, global, global, or structured system variable.
 * KVALUE::                              Kill only the value of a local, global, or structured system variable.  * KVALUE::                              Kill only the value of a local, global, or structured system variable.
 * LOCK::                                Control advisory locking for concurrency control.  * LOCK::                                Control advisory locking for concurrency control.
 * MAP::                                 Map a global name to a non-default namespace.  
 * MERGE::                               Merge contents of one local, global, or structured system variable into another.  * MERGE::                               Merge contents of one local, global, or structured system variable into another.
 * NEW::                                 Introduce a new scope for a specified local variable or intrinsic special variable or instantiate an object.  * NEW::                                 Introduce a new scope for a specified local variable or intrinsic special variable or instantiate an object.
 * OPEN::                                Open a sequential or socket input/output device.  * OPEN::                                Open a sequential or socket input/output device.
Line 2014  Identical to @ref{$TRANSLATE()}, except Line 2097  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.  * ZASSERT::                             Raise error when a conditional expression evaluates @emph{false}.
 * ZGO::                                 Unknown.  * ZBREAK::                              Enable/disable ZBREAK mode.
 * ZHALT::                               Unknown.  * ZCONST::                              Define a constant that cannot be altered after initial definition.
   * ZEDIT::                               Edit a routine using an external editor.
   * ZGOTO::                               @code{GOTO} with @code{BREAK} control.
   * ZHALT::                               Exit FreeM job with return value.
 * ZINSERT::                             Insert code into routine buffer.  * ZINSERT::                             Insert code into routine buffer.
 * ZJOB::                                Unknown.  * 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.
 * ZNEW::                                Unknown.  * ZNEW::                                Unknown.
 * ZPRINT::                              Print contents of routine buffer.  * ZPRINT::                              Print contents of routine buffer.
 * ZQUIT::                               Unknown.  * 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.
 * ZTRAP::                               Unknown.  * ZTHROW::                              Programmatically raise an error condition.
   * ZTRAP::                               Raise a FreeM error.
   * 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 2157  In its inclusive form, @code{ABLOCK} inc Line 2244  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 2333  In its argumentless form, @code{CLOSE} c Line 2385  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 2396  ELSE[@emph{:postcondition}] Line 2431  ELSE[@emph{:postcondition}]
 @quotation  @quotation
 @emph{Non-Standard Behavior}  @emph{Non-Standard Behavior}
   
 FreeM allows a @emph{postcondition} on @code{ELSE}. While explicitly forbidden in the @emph{standard}--and for good reason--it was decided that FreeM should allow postconditions everywhere, both for the sake of foolish consistency (the likes of which Emerson warned against), and for the benefit of entrants to a hypothetical future obfuscated M contest, and those with a Machiavellian predisposition to wicked perversions and undue cleverness.  FreeM allows a @emph{postcondition} on @code{ELSE}. While explicitly forbidden in the @emph{Standard}, it was decided that FreeM should allow postconditions everywhere, both for the sake of foolish consistency (the likes of which Emerson warned against), and for the benefit of entrants to a hypothetical future obfuscated M contest, and those with a Machiavellian predisposition to wicked perversions and undue cleverness.
   
 Using postconditions on @code{ELSE} should be strictly avoided in production code, as they have no practical use, and may contribute to technical debt, hardening of the arteries, hobgoblins, a small mind, a surfeit of logic, climate change, @emph{Daily WTF} rants, or the meltdown of global financial markets.  Using postconditions on @code{ELSE} should be strictly avoided in production code, as they have no practical use, and may contribute to technical debt, hardening of the arteries, hobgoblins, a small mind, a surfeit of logic, climate change, @emph{Daily WTF} rants, or the meltdown of global financial markets.
 @end quotation  @end quotation
Line 2551  IF[@emph{:postcondition}] @emph{tvexpr}[ Line 2586  IF[@emph{:postcondition}] @emph{tvexpr}[
   
 In its argumentless form, allows the remainder of the line of code following @code{IF} to execute only if @code{$TEST} evaluates to @emph{1}, provided the optional @emph{postcondition} evaluates to @emph{true} or is omitted.  In its argumentless form, allows the remainder of the line of code following @code{IF} to execute only if @code{$TEST} evaluates to @emph{1}, provided the optional @emph{postcondition} evaluates to @emph{true} or is omitted.
   
   
 @emph{Syntax}  @emph{Syntax}
 @example  @example
 IF[@emph{:postcondition}]  IF[@emph{:postcondition}]  @emph{command...}
 @end example  @end example
   
   @cartouche
   @quotation
   @emph{Style Recommendation}
   
   In the interest of readability and maintainability, we recommend avoiding the argumentless form of @code{IF} in new code. It is an obsolete relic of an era when routine sizes were severely limited, and can be difficult to spot, as the use of whitespace (@code{IF  @emph{command}}) makes the intent of its use non-obvious at a glance. It is also far too easy to inadvertently delete the extra space, leading to program errors easily avoided otherwise.
   
   We recommend explicitly checking the value of @code{$TEST} instead, as in @code{IF $TEST @emph{command}} or @code{@emph{command}:$TEST ...}, as this makes the intent immediately clear both to M newcomers and seasoned experts, and sacrifices nothing of value, even on the oldest computer systems where FreeM can be used today.
   @end quotation
   @end cartouche
   
 @node JOB  @node JOB
 @section JOB  @section JOB
 @cindex JOB  @cindex JOB
Line 2614  In the above @emph{inclusive} form, @cod Line 2660  In the above @emph{inclusive} form, @cod
 @cartouche  @cartouche
 @quotation  @quotation
 @emph{Note}  @emph{Note}
 The below @emph{argumentless} and @emph{exclusive} forms of @code{KSUBSCRIPTS} are not implemented in FreeM, as of version 0.64.0-rc1, but are planned for a future release.  The below @emph{argumentless} and @emph{exclusive} forms of @code{KSUBSCRIPTS} are not implemented in FreeM, as of version 0.65.1-rc1, but are planned for a future release.
 @end quotation  @end quotation
 @end cartouche  @end cartouche
   
Line 2649  In the above @emph{inclusive} form, @cod Line 2695  In the above @emph{inclusive} form, @cod
 @cartouche  @cartouche
 @quotation  @quotation
 @emph{Note}  @emph{Note}
 The below @emph{argumentless} and @emph{exclusive} forms of @code{KVALUE} are not implemented in FreeM, as of version 0.64.0-rc1, but are planned for a future release.  The below @emph{argumentless} and @emph{exclusive} forms of @code{KVALUE} are not implemented in FreeM, as of version 0.65.1-rc1, but are planned for a future release.
 @end quotation  @end quotation
 @end cartouche  @end cartouche
   
Line 2705  If @code{LOCK} succeeds within @emph{tim Line 2751  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 2969  Saves the value of @code{$TEST} until th Line 3000  Saves the value of @code{$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 3054  If you are using more than one transacti Line 3064  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 3372  VIEW 133:@emph{tvexpr} Line 3368  VIEW 133:@emph{tvexpr}
   
 @end table  @end table
   
 @node WATCH  
 @section WATCH  
 @cindex WATCH  @node WRITE
 @cindex commands, WATCH  @section WRITE
   @cindex WRITE
   @cindex commands, WRITE
   
   @node XECUTE
   @section XECUTE
   @cindex XECUTE
   @cindex commands, XECUTE
   
   @node ZASSERT
   @section ZASSERT
   @cindex ZASSERT
   @cindex commands, ZASSERT
 @cindex commands, debugging  @cindex commands, debugging
 @cindex commands, implementation-specific  @cindex commands, implementation-specific
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
 Sets a watchpoint on a global, local, or SSVN node.  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.
   
 @emph{Syntax}  
   
   The @code{ZASSERT} error is catchable whether using standard-style, FreeM-style, or DSM 2.0-style error processing.
   
 In its @emph{argumentless} form, @code{WATCH} toggles watchpoints on and off, provided the optional @emph{postcondition} is @emph{true} or omitted.  @emph{Syntax}
   
 @example  @example
 WATCH[@emph{:postcondition}]   ZASSERT@emph{:postcondition} @emph{<tvexpr>}
 @end example  @end example
   
 In its @emph{inclusive} form, @code{WATCH} adds, removes, or examines watchpoints, provided the optional @emph{postcondition} is @emph{true} or omitted.  @emph{Example}
   
 A @code{+} adds a new watchpoint to the following variable.  @example
   DEFAULT.USER> SET DEBUG=1
   
 A @code{-} removes an existing watchpoint for the following variable.  
   
 A @code{?} examines the status of a watchpoint for the following variable.  DEFAULT.USER> ZASSERT:DEBUG 1=1
   
 @example  
 WATCH[@emph{:postcondition}] [+|-|?]@emph{var1}...,[+|-|?]@emph{varN}  DEFAULT.USER> ZASSERT:DEBUG 1=0
    
    
   >> Error ZASSERT:  programmer assertion failed in SYSTEM::^%SYSINIT  [$STACK = 0]
   >> ZASSERT:DEBUG 1=0
                      ^
 @end example  @end example
   
   @node ZBREAK
   @section ZBREAK
   @cindex ZBREAK
   @cindex commands, ZBREAK
   @cindex commands, debugging
   @cindex commands, implementation-specific
   @cindex commands, non-standard
   @emph{FreeM Extension}
   
 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)}.  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}.
   
 @example  @emph{Syntax}
 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)  
   
   @example
   ZBREAK @emph{tvexpr}
 @end example  @end example
   
 The following example will remove that watchpoint:  @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  @example
 DEFAULT.USER> WATCH -^SNW(1)  @code{ZCONST@emph{:postcondition} @emph{mref1}=@emph{initial-value1},...,@emph{mrefN}=@emph{initial-valueN}}
    
 Removed '^SNW("1")' from the watchlist.  
    
 DEFAULT.USER> WATCH ?^SNW(1)  
    
 '^SNW("1")' is not being watched.  
 @end example  @end example
   
 @node WITH  @node ZEDIT
 @section WITH  @section ZEDIT
 @cindex WITH  @cindex ZEDIT
 @cindex commands, WITH  @cindex commands, ZEDIT
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
 NOTE: This command may be deprecated and removed in future FreeM releases.  Edits a routine using an external editor. Uses environment variable @code{$EDITOR} if defined; otherwise, uses @code{vi}.
   
 Sets a prefix to be applied to all subsequent local variable or constant references.  
   
 @emph{Syntax}  @emph{Syntax}
   
 @example  @example
 @code{WITH@emph{:postcondition} @emph{var-prefix}}  ZEDIT@emph{[:postcondition]}
 @end example  @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.  In its argumentless form, edits the currently-active routine, provided the optional @emph{postcondition} is @emph{true} or omitted.
   
 The @emph{var-prefix} argument may be a string literal or any valid FreeM expression.  @emph{Syntax}
   
 @example  @example
 @code{WITH@emph{:postcondition}}  ZEDIT@emph{[:postcondition]} @emph{<routine-name>}
 @end example  @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 ""}.  In its single-argument form, edits @emph{<routine-name>}, provided the optional @emph{postcondition} is @emph{true} or omitted.
   
   If the specified routine does not exist, it will be created.
   
 @node WRITE  Routine names must not be quoted, and must not included a leading caret (@code{^}).
 @section WRITE  
 @cindex WRITE  
 @cindex commands, WRITE  
   
 @node XECUTE  @emph{Errors}
 @section XECUTE  
 @cindex XECUTE  
 @cindex commands, XECUTE  
   
 @node ZBREAK  @code{ZEDIT} will raise @code{ZNOPGM} in its argumentless form if there is no routine currently loaded.
 @section ZBREAK  
 @cindex ZBREAK  
 @cindex commands, ZBREAK  
 @cindex commands, debugging  
 @cindex commands, implementation-specific  
 @cindex commands, non-standard  
 @emph{FreeM Extension}  
   
 @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 single-argument form, enables @code{BREAK} mode and branches unconditionally to @emph{entryref}.
   
   @emph{Syntax}
   
   @example
   ZGOTO @emph{entryref}
   @end example
   
   In its argumentless 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 3497  In the above argumentless form, clears t Line 3515  In the above argumentless form, clears t
 @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 3505  In the above argumentless form, clears t Line 3539  In the above argumentless form, clears t
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
   Inserts a line of M code into the currently-active routine buffer, provided the optional @emph{postcondition} is @emph{true} or omitted.
   
   @emph{Syntax}
   
   @example
   ZINSERT@emph{:postcondition} @emph{expr V mcode}[:@emph{label}]
   @end example
   
   Above, @emph{expr V mcode} is an expression returning a string giving M code. If @emph{label} is omitted, the code will be inserted at the insertion point, which is typically the end of the routine. Otherwise, the code will be inserted at the line immediately following @emph{label}.
   
 @node ZJOB  @node ZJOB
 @section ZJOB  @section ZJOB
 @cindex ZJOB  @cindex ZJOB
Line 3533  Loads routine @emph{<routine-name>} into Line 3577  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 3549  ZLOAD@emph{:postcondition} @emph{<routin Line 3609  ZLOAD@emph{:postcondition} @emph{<routin
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
 Prints the contents of the current routine buffer, provided the optional @emph{postcondition} is @emph{true} or omitted.  In argumentless form, prints the contents of the current routine buffer, provided the optional @emph{postcondition} is @emph{true} or omitted.
   
 @emph{Syntax}  @emph{Syntax}
   
Line 3557  Prints the contents of the current routi Line 3617  Prints the contents of the current routi
 ZPRINT@emph{:postcondition}  ZPRINT@emph{:postcondition}
 @end example  @end example
   
   In argumented form, prints a subset of the current routine buffer, provided the optional @emph{postcondition} is @emph{true} or omitted.
   
   @emph{Syntax}
   
   @example
   ZPRINT@emph{:postcondition} @emph{start}[:@emph{end}]
   @end example
   
   In the above syntax, @emph{start} and @emph{end} can be a tag in the current routine, or @code{*} to indicate the routine buffer insertion point (typically the end of the routine).
   
 @node ZQUIT  @node ZQUIT
 @section ZQUIT  @section ZQUIT
 @cindex ZQUIT  @cindex ZQUIT
Line 3583  In its argumentless form, quits from @co Line 3653  In its argumentless form, quits from @co
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
   In argumentless form, removes all M code from the current routine buffer, provided the optional @emph{postcondition} is @emph{true} or omitted.
   
   @emph{Syntax}
   
   @example
   ZREMOVE@emph{:postcondition}
   @end example
   
   In argumented form, removes a subset of the current routine buffer, provided the optional @emph{postcondition} is @emph{true} or omitted.
   
   @emph{Syntax}
   
   @example
   ZREMOVE@emph{:postcondition} @emph{start}[:@emph{end}]
   @end example
   
   In the above syntax, @emph{start} and @emph{end} can be a tag in the current routine, or @code{*} to indicate the routine buffer insertion point (typically the end of the routine).
   
 @node ZSAVE  @node ZSAVE
 @section ZSAVE  @section ZSAVE
 @cindex ZSAVE  @cindex ZSAVE
Line 3591  In its argumentless form, quits from @co Line 3679  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 3600  In its argumentless form, quits from @co Line 3710  In its argumentless form, quits from @co
 @cindex commands, non-standard  @cindex commands, non-standard
 @emph{FreeM Extension}  @emph{FreeM Extension}
   
   Synonymous with @ref{ZTHROW}.
   
   @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 4542  SET MYSTRING="This is a ""string literal Line 4765  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 4664  Transaction processing allows applicatio Line 4887  Transaction processing allows applicatio
 @section Transaction Processing  @section Transaction Processing
 @cindex transaction processing  @cindex transaction processing
   
 FreeM implements a significant subset of the transaction processing features from @emph{ANSI X11.1-1995}. This allows a series of global operations to be conducted all at once, either in batch mode (where concurrency is not disturbed), or in serial mode (where writes are guaranteed to be atomic, consistent, isolated, and durable).  FreeM implements a significant subset of the transaction processing features from @emph{ANSI X11.1-1995}. This allows a series of global operations to be conducted all at once, either in batch mode (where concurrent operation is not interrupted until the last possible moment), or in serial mode (where writes are guaranteed to be atomic, consistent, isolated, and durable).
   
 @subsection Theory of Operation  @subsection Theory of Operation
   
Line 4743  The effect of this is that the operation Line 4966  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
   
   FreeM @emph{local variables} have the same data structure as global variables, but are scoped to a single FreeM process, and stored in memory.
   
   Each local comprises three elements:
   
   @itemize @bullet
   @item
   An alphabetic name beginning with a letter or a percent sign (@code{%})
   @item
   Optionally, one or more comma-delimited subscripts, enclosed in parentheses
   @item
   A value of up to 255 characters in length
   @end itemize
   
   @node Creating Local Variables
   @section Creating Local Variables
   @cindex local variables, creating
   
   To create a local variable, use the @code{SET} command:
   
   @example
   SET MYLOCAL("foo","bar")="this is the data value"
   @end example
   
   @node Removing Local Variables
   @section Removing Local Variables
   @cindex local variables, removing
   
   To remove an entire local variable, you can use the @code{KILL} command with the unsubscripted name of the variable:
   
   @example
   KILL MYLOCAL
   @end example
   
   If you only want to remove part of a local variable, i.e., beginning at a certain subscript level, use the @code{KILL} command with a subscripted name:
   
   @example
   KILL MYLOCAL("foo")
   @end example
   
   This will remove only the @code{"foo"} subscript and all of its children.
   
   If you only want to remove the data value at a specific subscript level, leaving the subscript itself intact, use @code{KVALUE}:
   
   @example
   KVALUE MYLOCAL("foo")
   @end example
   
 @node Scoping  @node Scoping
 @chapter Scoping  @chapter Scoping
 @cindex scoping  @cindex scoping
   
   By default, FreeM local variables and their values are scoped to the entire process, meaning that any function or subroutine can access and modify their values. This can lead to pernicious bugs.
   
   M provides the @code{NEW} command to work around these issues. When @code{NEW} is called with a local variable as its argument, FreeM will scope the variable to the process stack frame in which the @code{NEW} command occured. When exiting the stack frame (i.e. with the @code{QUIT} command), FreeM will restore the variable to its value prior to being @code{NEW}ed.
   
   @emph{Example}
   
   @example
   MYRTN ;
     S J=1 ; set local variable J to 1
     W J,! ; this will output "1"
     D X   ; execute subroutine X
     W J,! ; this will output "1", as the value of J was restored
     Q
     ;;
   X ;
     N J   ; stack J
     S J=6 ; set its value to 6
     W J,! ; this will output "6"
     Q     ; quit from the subroutine, destroying its stack frame
     ;;
   @end example
   
   @section Scoping Considerations for $TEST
   
   In M, the truth value of comparisons, logic operations, and certain forms of @code{LOCK} is stored in the @code{$TEST} intrinsic special variable, which follows the same rules as any M local variable.
   
   This is probably the most significant design flaw of the language, as the side effects of logic on @code{$TEST} lead to incredibly difficult bugs. However, M allows @code{$TEST} to be @code{NEW}ed, and FreeM provides the @code{THEN} command@footnote{From MDC Type A extension X11/1998-31} to help in the case of conditionals. @code{THEN} stacks @code{$TEST} to the end of the line.
   
   When writing new M code in FreeM, we strongly suggest using @code{THEN} as follows:
   
   @example
   MYRTN ;
     IF MYVAR=1 THEN DO SUBRT
   @end example
   
   This is instead of the traditional form:
   
   @example
   MYRTN ;
     IF MYVAR=1 DO SUBR
   @end example
   
   @cartouche
   @quotation
   @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.
   
   If you use other M implementations, you should bug the implementers to implement @code{THEN}, as it at least partially mitigates an inexcusable flaw in the design of M.
   @end quotation
   @end cartouche
   
 @node Decision Constructs  @node Decision Constructs
 @chapter Decision Constructs  @chapter Decision Constructs
 @cindex decision constructs  @cindex decision constructs
Line 4790  The effect of this is that the operation Line 5121  The effect of this is that the operation
 @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 4826  DESTROY(THIS) ; This is the destructor Line 5147  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 4851  A constructor looks like this: Line 5171  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 4878  Inheritance is achieved by specifying th Line 5197  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 4908  DEFAULT.USER> W MYOBJ.MYMETHOD() Line 5226  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 4942  NEW MYSTR=$#^%STRING("myString") Line 5260  NEW MYSTR=$#^%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 5540  Raised when you attempt to use multiple Line 5857  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}.
Line 5738  Raised when an attempt is made to use a Line 6055  Raised when an attempt is made to use a
 FreeM allows the following installation methods:  FreeM allows the following installation methods:
 @table @asis  @table @asis
 @item Binary Repository  @item Binary Repository
 On recent versions the Ubuntu and Debian distributions of GNU/Linux, we provide package repositories from which FreeM may easily be installed. See the @emph{FreeM Wiki} for more information, and @emph{https://packages.coherent-logic.com} for instructions.  For recent versions of the Ubuntu and Debian distributions of GNU/Linux, we provide package repositories from which FreeM may easily be installed. See the @emph{FreeM Wiki} for more information, and @emph{https://packages.coherent-logic.com} for instructions.
   
 If available, this is the simplest method of installing FreeM.  If available, this is the simplest method of installing FreeM.
 @item Binary Packages  @item Binary Packages
 We provide binary packages of FreeM for @emph{dpkg} and @emph{rpm}-based distributions of GNU/Linux, and @emph{pkgadd} packages for Solaris 8-10. If you cannot use repositories, this is the easiest option.  We provide binary packages of FreeM for @emph{dpkg} and @emph{rpm}-based distributions of GNU/Linux, and @emph{pkgadd} packages for Solaris 8-10. If you cannot use repositories, this is the easiest option.
   
 See @emph{https://freem.coherent-logic.com/binaries.cfm} for downloads and instructions.  See @emph{https://freem.coherent-logic.com/binaries.cfm} for downloads and instructions.
 @item Source Archive  @item Source Tarball
 If you prefer installing from source, we recommend that you download the latest @emph{.tar.gz} file from @emph{https://freem.coherent-logic.com/downloads.cfm}, and follow these steps:  If you prefer installing from source, we recommend that you download the latest @emph{.tar.gz} file from @emph{https://freem.coherent-logic.com/downloads.cfm}, and follow these steps:
   
 @example  @example
Line 5798  $ make Line 6115  $ make
 $ sudo make install  $ sudo make install
 @end example  @end example
   
   @item @code{--enable-newglobals} (EXPERIMENTAL)
   Enables a new and modernized global handler. This global handler has a number of known bugs, and thus should be used with caution.
   
   Note that global files created in the default global handler are incompatible with the new global handler, and vice-versa. You will need to back up and remove all globals in your environments when switching global handlers.
   
   
   @emph{Example}
   
   @example
   $ ./configure --enable-newglobals
   $ make
   $ sudo make install
   @end example
   
 @end table  @end table
   
 @subsection Initial Configuration  @subsection Initial Configuration
Line 6256  int main(int argc, char **argv, char **e Line 6587  int main(int argc, char **argv, char **e
 @cindex fmadm  @cindex fmadm
   
 The @code{fmadm} utility is the preferred method of managing a FreeM installation, and will eventually replace all of the existing utilities.  The @code{fmadm} utility is the preferred method of managing a FreeM installation, and will eventually replace all of the existing utilities.
 Unlike the existing, legacy utilities, @code{fmadm} presents a consistent, simple interface for all FreeM management tasks, and is namespace-aware.  In support of FreeM operators, @code{fmadm} presents a consistent, simple interface for all FreeM management tasks, and is namespace-aware.
 This appendix will document each @code{fmadm} facility as it is implemented, until all of the legacy utilities have been replaced.  This appendix will document each @code{fmadm} facility as it is implemented.
   
 The @code{fmadm} utility's functions all follow the below, consistent syntax:  The @code{fmadm} utility's functions all follow the below, consistent syntax:
   
Line 6351  Supported actions are @code{list} and @c Line 6682  Supported actions are @code{list} and @c
 @end table  @end table
   
   
 @node FreeM Legacy Utilities  
 @appendix FreeM Legacy Utilities  
 @cindex utilities, legacy  
   
 @section Global Compactor (gcompact)  
 @cindex utilities, legacy, gcompact  
   
 Compacts the specified global in place.  
   
 @emph{Syntax}  
   
 @example  
 gcompact @emph{/path/to/global/file}  
 @end example  
   
 @section Block Examiner (gfix)  
 @cindex utilities, gfix  
   
 The @emph{gfix} interactive utility program permits navigation of the B-tree structure of the specified global a block at a time.  
   
 @emph{Syntax}  
   
 @example  
 gfix @emph{</path/to/global/file>}  
 @end example  
   
 @section Global Repair Tool (grestore)  
 @cindex utilities, legacy, grestore  
   
 This utility will fix problems with the specified global.  
   
 @emph{Syntax}  
   
 @example  
 grestore @emph{</path/to/global/file>}  
 @end example  
   
 @node FreeM VIEW Commands and Functions  @node FreeM VIEW Commands and Functions
 @appendix FreeM VIEW Commands and Functions  @appendix FreeM VIEW Commands and Functions
   
Removed from v.1.36  
changed lines
  Added in v.1.63

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