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-version 1.36, 2025/05/02 14:35:40
+version 1.56, 2025/05/16 13:22:58
  Line 4
  @settitle The FreeM Manual
  @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-rc0), 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
  Line 19  Permission is granted to copy, distribut
  @title The FreeM Manual
  @subtitle @sc{The Official Manual of FreeM}
- @subtitle Version 0.64.0-rc1
+ @subtitle Version 0.65.1-rc0
  @c@vskip 10pt
  @c@center @image{freem-logo-sm,,,,.png}
  @author Serena Willis
  Line 44  This is the official manual for the Free
  @menu
  * Introduction::                        About the FreeM Project, its history, and its goals.
  * 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.
  * The FreeM Environment Daemon::        Managing shared resources in the FreeM environment.
  * The FreeM Direct-Mode Environment::   Executing M programs interactively.
- Line 99  This is the official manual for the Free
+ Line 100  This is the official manual for the Free
  * Accessing FreeM from C Programs::     How to use the mlib interface.
  * 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.
  * Implementation Limits::               FreeM limitations.
  * US-ASCII Character Set::              The US-ASCII character set.
  Line 117  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.
+ For more information on FreeM history, see @code{@emph{$PREFIX}/share/freem/doc/freem_history.*} (distributed in PostScript, PDF, and plain text formats).
  @section Production Readiness
  FreeM is not yet production-ready. There are several show-stopping bugs that preclude a general release for public use:
- Line 146  Current contributors denoted with a @emp
+ Line 148  Current contributors denoted with a @emp
  @cindex contributors, Gerum, Winfried
  @cindex contributors, Kreis, Greg
  @cindex contributors, Landis, Larry
+ @cindex contributors, McGlothlen, Ken
  @cindex contributors, Milligan, Lloyd
  @cindex contributors, Morris, Steve
  @cindex contributors, Murray, John
- Line 187  Larry Landis (Coordination, Code, Docume
+ Line 190  Larry Landis (Coordination, Code, Docume
  Rick Marshall (Testing, MDC Conformance) @emph{+}
  @item
+ Ken McGlothlen (Apple Silicon build/test environment, proofreading of documentation) @emph{+}
+ @item
  Lloyd Milligan (Code, Testing, Documentation)
  @item
- Line 248  FreeM uses abbreviations for common lang
+ Line 254  FreeM uses abbreviations for common lang
  @table @asis
  @item @emph{$PREFIX}
  Refers to the base filesystem location within which FreeM is installed. For most distribution methods of FreeM, @emph{$PREFIX} represents either @code{/} or @code{/usr/local}.
+ @item @emph{dlabel}
+ Refers to a label in an M routine, beginning in the first column of the line. Can be a @emph{name} or an @emph{intlit}.
+ @item @emph{entryref}
+ Refers to an M routine entry point, denoted in the format @code{@emph{dlabel} [+@emph{intexpr}][^@emph{routine}]}.
  @item @emph{expr}
  Refers to any expression. Often presented in the format @emph{expr V <type>}, where @emph{V} means @emph{giving}; e.g., @emph{expr V lvn} means @emph{expression giving local variable name}.
  @item @emph{glvn}
- Line 256  Refers to the name of an M global, local
+ Line 266  Refers to the name of an M global, local
  Refers to the name of an M global variable.
  @item @emph{intexpr}
  Refers to an integer expression.
+ @item @emph{intlit}
+ Refers to an integer literal.
  @item @emph{ISV}, @emph{isv}
  Refers to an M intrinsic special variable; @code{$JOB} and @code{$IO} are examples of ISVs.
  @item @emph{L}
  Indicates a @emph{list} of the following item, e.g., @emph{L gvn} means @emph{list of global variable names}.
  @item @emph{lvn}
  Refers to the name of an M local variable.
+ @item @emph{postcondition}
+ A @emph{tvexpr} immediately following a command verb affecting that command's execution.
+ @item @emph{strlit}
+ Refers to an M string literal.
  @item @emph{ssvn}
  Refers to the name of an M structured system variable.
  @item @emph{tvexpr}
- Refers to a truth-valued expression.
+ Refers to a truth-valued expression, i.e., an expression interpreted as a truth value.
  @end table
+ @node A Note on Standards
+ @chapter A Note on Standards
+ @cindex MDC
+ @cindex M Development Committee
+ @cindex ANSI X11.1
+ @cindex standards, ANSI
+ @cindex standards, MDC
+ FreeM attempts to implement as many features as possible from the M Development Committee's unpublished @emph{Millennium Draft Standard}, as well as its predecessors.
+ The maintainer of FreeM (who is also the author of this book) is largely in favor of standardization efforts, and hopes that the MDC will resume activities, and will happily participate if it does so in an open, public, transparent, and democratic manner. Until then, however, FreeM will attempt to improve the M language, in cooperation with other free software M implementers where possible. Any breaking changes introduced in future MDC releases of the @emph{Standard} (such as the rumored @emph{M5}) which prove incompatible with FreeM will be handled via the @code{$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
  @chapter FreeM Invocation
  @cindex invocation, command-line
- Line 414  Attempting to start a FreeM interpreter
+ Line 444  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>}}:
  @example
- Coherent Logic Development FreeM version 0.64.0-rc1 (x86_64-pc-linux-gnu)
+ Coherent Logic Development FreeM version 0.65.1-rc0 (x86_64-pc-linux-gnu)
  Copyright (C) 2014, 2020, 2021 Coherent Logic Development LLC
- Line 673  Please note that FreeM is not entirely s
+ Line 703  Please note that FreeM is not entirely s
  * $SYSTEM::                  MDC system ID of FreeM.
  * $TEST::                    Truth value of last conditional expression or result of certain @code{LOCK} operations.
  * $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.
  * $Y::                       Current vertical screen position.
  * $ZA::                      Current position of file on @code{$IO}.
- Line 869  uncommitted transactions exist.
+ Line 899  uncommitted transactions exist.
  @cindex $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
  @section $X
- Line 1088  See @emph{https://wiki.osdev.org/Target_
+ Line 1118  See @emph{https://wiki.osdev.org/Target_
  * $ZLSD()::                             Compute Levenshtein distance between two arguments.
  * $ZM()::                               Unknown.
  * $ZNAME()::                            Unknown.
- * $ZNEXT()::                            Unknown.
+ * $ZNEXT()::                            Return glvn of next numeric subscript following given glvn.
  * $ZORDER()::                           Unknown.
  * $ZPIECE()::                           Unknown.
  * $ZPREVIOUS()::                        Unknown.
- Line 1286  The optional second argument indicates t
+ Line 1316  The optional second argument indicates t
  @cindex intrinsic functions, $NEXT
  Deprecated. Use @code{$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()
  @section $ORDER
- Line 1686  Returns the Levenshtein distance between
+ Line 1738  Returns the Levenshtein distance between
  @cindex intrinsic functions, $ZM
  @cindex intrinsic functions, implementation-specific
+ Purpose unknown.
  @node $ZNAME()
  @section $ZNAME
  @cindex $ZNAME
- Line 1694  Returns the Levenshtein distance between
+ Line 1748  Returns the Levenshtein distance between
  Purpose unknown.
+ This function relies on the value of @code{$VIEW(71)} being @code{0} (this is not the default).
  @node $ZNEXT()
  @section $ZNEXT
  @cindex $ZNEXT
  @cindex intrinsic functions, $ZNEXT
  @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()
  @section $ZORDER
- Line 1986  Identical to @ref{$TRANSLATE()}, except
+ Line 2065  Identical to @ref{$TRANSLATE()}, except
  * !::                                   Run an external program or command.
  * !!::                                  Launch a subshell from FreeM direct mode.
  * ABLOCK::                              Increment the block counter for one or more event classes.
- * ASSERT::                              Raise error when a conditional expression evaluates @emph{false}.
  * ASTART::                              Enable asynchronous event handling for one or more event classes.
  * ASTOP::                               Disable asynchronous event handling for one or more event classes.
  * AUNBLOCK::                            Decrement the block counter for one or more event classes.
  * BREAK::                               Interrupt a running routine to allow interactive debugging.
  * CLOSE::                               Close an input/output device.
- * CONST::                               Define a constant that cannot be altered after initial definition.
  * DO::                                  Transfer program control to one or more subroutines or introduces a new execution level.
  * ELSE::                                Execute the remainder of a line if @code{@ref{$TEST}} evaluates @emph{false}.
  * FOR::                                 Repeat execution of a line or block of code.
- Line 2005  Identical to @ref{$TRANSLATE()}, except
+ Line 2082  Identical to @ref{$TRANSLATE()}, except
  * 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.
  * 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.
  * 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.
- Line 2014  Identical to @ref{$TRANSLATE()}, except
+ Line 2090  Identical to @ref{$TRANSLATE()}, except
  * SET::                                 Set the value of a local variable, global, intrinsic special variable, or structured system variable.
  * TCOMMIT::                             Commit a transaction.
  * THEN::                                Preserve @code{@ref{$TEST}} until the end of the current line.
- * THROW::                               Programmatically raise an error condition.
  * TROLLBACK::                           Roll back all pending transactions.
  * 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.
  * 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.
  * 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.
+ * ZGOTO::                               @code{GOTO} with @code{BREAK} control.
+ * ZHALT::                               Exit FreeM job with return value.
  * ZINSERT::                             Insert code into routine buffer.
- * ZJOB::                                Unknown.
+ * ZJOB::                                Invoke job, ignoring any timeouts.
  * ZLOAD::                               Load routine into routine buffer.
+ * ZMAP::                                Map a global name to a non-default namespace.
  * ZNEW::                                Unknown.
  * ZPRINT::                              Print contents of routine buffer.
- * ZQUIT::                               Unknown.
+ * ZQUIT::                               Quit multiple stack levels at once.
  * ZREMOVE::                             Remove code from routine buffer.
  * 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}}.
  @end menu
- Line 2157  In its inclusive form, @code{ABLOCK} inc
+ Line 2236  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.
- @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
  @section ASTART
- Line 2333  In its argumentless form, @code{CLOSE} c
+ Line 2377  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.
- @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
  @section DO
  @cindex DO
- Line 2396  ELSE[@emph{:postcondition}]
+ Line 2423  ELSE[@emph{:postcondition}]
  @quotation
  @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.
  @end quotation
- Line 2551  IF[@emph{:postcondition}] @emph{tvexpr}[
+ Line 2578  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.
  @emph{Syntax}
  @example
- IF[@emph{:postcondition}]
+ IF[@emph{:postcondition}]  @emph{command...}
  @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
  @section JOB
  @cindex JOB
- Line 2614  In the above @emph{inclusive} form, @cod
+ Line 2652  In the above @emph{inclusive} form, @cod
  @cartouche
  @quotation
  @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-rc0, but are planned for a future release.
  @end quotation
  @end cartouche
- Line 2649  In the above @emph{inclusive} form, @cod
+ Line 2687  In the above @emph{inclusive} form, @cod
  @cartouche
  @quotation
  @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-rc0, but are planned for a future release.
  @end quotation
  @end cartouche
- Line 2705  If @code{LOCK} succeeds within @emph{tim
+ Line 2743  If @code{LOCK} succeeds within @emph{tim
  LOCK[@emph{:postcondition}] @emph{name}[:@emph{timeout}][,...@emph{name}[:@emph{timeout}]]
  @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
  @section MERGE
  @cindex MERGE
- Line 2969  Saves the value of @code{$TEST} until th
+ Line 2992  Saves the value of @code{$TEST} until th
  IF 1 THEN  WRITE "HELLO!",!
  @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
  @section TROLLBACK
  @cindex TROLLBACK
- Line 3054  If you are using more than one transacti
+ Line 3056  If you are using more than one transacti
  TSTART (FOO,BAR):(SERIAL,TRANSACTIONID="FOO")
  @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
  @section USE
- Line 3372  VIEW 133:@emph{tvexpr}
+ Line 3360  VIEW 133:@emph{tvexpr}
  @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, implementation-specific
  @cindex commands, non-standard
  @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.
+ @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}]
+  ZASSERT@emph{:postcondition} @emph{<tvexpr>}
  @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.
- 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}
+ DEFAULT.USER> SET DEBUG=1
- @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)}.
+ DEFAULT.USER> ZASSERT:DEBUG 1=1
- @example
- DEFAULT.USER> WATCH
+ DEFAULT.USER> ZASSERT:DEBUG 1=0
- 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)
+ >> Error ZASSERT:  programmer assertion failed in SYSTEM::^%SYSINIT  [$STACK = 0]
+ >> ZASSERT:DEBUG 1=0
+                    ^
  @end example
- The following example will remove that watchpoint:
+ @node ZBREAK
+ @section ZBREAK
+ @cindex ZBREAK
+ @cindex commands, ZBREAK
+ @cindex commands, debugging
+ @cindex commands, implementation-specific
+ @cindex commands, non-standard
+ @emph{FreeM Extension}
+ Sets or clears the @code{ZBREAK} flag@footnote{NOTE: FreeM team needs to investigate how @code{zbreakon} and @code{zbflag} affect program execution.}, based on the result of evaluating @emph{tvexpr}.
+ @emph{Syntax}
  @example
- DEFAULT.USER> WATCH -^SNW(1)
+ ZBREAK @emph{tvexpr}
- Removed '^SNW("1")' from the watchlist.
- DEFAULT.USER> WATCH ?^SNW(1)
- '^SNW("1")' is not being watched.
  @end example
- @node WITH
+ @node ZCONST
- @section WITH
+ @section ZCONST
- @cindex WITH
+ @cindex ZCONST
- @cindex commands, WITH
+ @cindex commands, ZCONST
  @cindex commands, non-standard
  @emph{FreeM Extension}
- NOTE: This command may be deprecated and removed in future FreeM releases.
+ Defines a local @emph{constant}, or variable that cannot be altered after its initial definition, provided the optional @emph{postcondition} is @emph{true} or omitted.
- Sets a prefix to be applied to all subsequent local variable or constant references.
+ Constants must only be locals, and globals are not supported.
  @emph{Syntax}
  @example
- @code{WITH@emph{:postcondition} @emph{var-prefix}}
+ @code{ZCONST@emph{:postcondition} @emph{mref1}=@emph{initial-value1},...,@emph{mrefN}=@emph{initial-valueN}}
  @end example
- In the above single-argument form, sets the @code{$WITH} prefix to @emph{var-prefix}, provided that the optional @emph{postcondition} is either @emph{true} or omitted.
+ @node ZGOTO
+ @section ZGOTO
+ @cindex ZGOTO
+ @cindex commands, ZGOTO
+ @cindex commands, implementation-specific
+ @cindex commands, non-standard
+ @emph{FreeM Extension}
- The @emph{var-prefix} argument may be a string literal or any valid FreeM expression.
+ In its argumented form, enables @code{BREAK} mode and branches unconditionally to @emph{entryref}.
+ @emph{Syntax}
  @example
- @code{WITH@emph{:postcondition}}
+ ZGOTO @emph{entryref}
  @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 argumented form, resumes execution after a @code{BREAK}.
- @node WRITE
+ @emph{Syntax}
- @section WRITE
- @cindex WRITE
- @cindex commands, WRITE
- @node XECUTE
- @section XECUTE
- @cindex XECUTE
- @cindex commands, XECUTE
- @node ZBREAK
- @section ZBREAK
- @cindex ZBREAK
- @cindex commands, ZBREAK
- @cindex commands, debugging
- @cindex commands, implementation-specific
- @cindex commands, non-standard
- @emph{FreeM Extension}
- @node ZGO
+ @example
- @section ZGO
+ ZGOTO
- @cindex ZGO
+ @end example
- @cindex commands, ZGO
- @cindex commands, implementation-specific
- @cindex commands, non-standard
- @emph{FreeM Extension}
  @node ZHALT
  @section ZHALT
- Line 3497  In the above argumentless form, clears t
+ Line 3474  In the above argumentless form, clears t
  @cindex commands, non-standard
  @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
  @section ZINSERT
  @cindex ZINSERT
- Line 3533  Loads routine @emph{<routine-name>} into
+ Line 3526  Loads routine @emph{<routine-name>} into
  ZLOAD@emph{:postcondition} @emph{<routine-name>}
  @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
  @section ZNEW
  @cindex ZNEW
- Line 3591  In its argumentless form, quits from @co
+ Line 3600  In its argumentless form, quits from @co
  @cindex commands, non-standard
  @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
  @section ZTRAP
  @cindex ZTRAP
- Line 3600  In its argumentless form, quits from @co
+ Line 3631  In its argumentless form, quits from @co
  @cindex commands, non-standard
  @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
  @section ZWRITE
  @cindex ZWRITE
- Line 4542  SET MYSTRING="This is a ""string literal
+ Line 4686  SET MYSTRING="This is a ""string literal
  @cindex types, custom
  @cindex classes
- See @ref{Classes}.
+ See @ref{Object-Oriented Programming}.
  @node Globals
  @chapter Globals
- Line 4664  Transaction processing allows applicatio
+ Line 4808  Transaction processing allows applicatio
  @section 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
- Line 4743  The effect of this is that the operation
+ Line 4887  The effect of this is that the operation
  @cindex variables, local
  @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
  @chapter 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
  @chapter Decision Constructs
  @cindex decision constructs
- Line 4790  The effect of this is that the operation
+ Line 5042  The effect of this is that the operation
  @cindex programming, object-oriented
  @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
  @node 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
  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 5068  DESTROY(THIS) ; This is the destructor
  The above example demonstrates general class syntax.
- @node Constructors
  @subsection Constructors
  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 5092  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}.
- @node 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}).
- Line 4878  Inheritance is achieved by specifying th
+ Line 5118  Inheritance is achieved by specifying th
  CLASS(THIS,INIT):SUPERCLASS
  @end example
- @node 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.
- Line 4908  DEFAULT.USER> W MYOBJ.MYMETHOD()
+ Line 5147  DEFAULT.USER> W MYOBJ.MYMETHOD()
  VALUE
  @end example
  @node 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.
- Line 4942  NEW MYSTR=$#^%STRING("myString")
+ Line 5181  NEW MYSTR=$#^%STRING("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:
- Line 5540  Raised when you attempt to use multiple
+ Line 5778  Raised when you attempt to use multiple
  Raised when attempts are made to set @code{$ECODE} to an invalid error code value. Obsolete and replaced by standard error code @code{M101}.
  @item @code{ZASSERT} - @emph{programmer assertion failed}
- Raised when an @code{ASSERT} expression's result is not true.
+ Raised when an @code{ZASSERT} expression's result is not true.
  @item @code{ZUSERERR} - @emph{user-defined error}
  Raised when program code calls @code{THROW} with an error code argument for which the first character is @code{U}, or when @code{$ECODE} is set to an error code for which the first character is @code{U}.
- Line 6256  int main(int argc, char **argv, char **e
+ Line 6494  int main(int argc, char **argv, char **e
  @cindex fmadm
  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:
- Line 6351  Supported actions are @code{list} and @c
+ Line 6589  Supported actions are @code{list} and @c
  @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
  @appendix FreeM VIEW Commands and Functions

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