freem/doc/freem.texi - diff

Return to freem.texi CVS log

Up to [Coherent Logic Development] / freem / doc

Diff for /freem/doc/freem.texi between versions 1.36 and 1.43

-version 1.36, 2025/05/02 14:35:40
+version 1.43, 2025/05/05 04:55:42
  Line 7
  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:
  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 44  This is the official manual for the Free
+ Line 45  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 117  When GT.M was open-sourced in late 1999,
+ Line 119  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{$PREFIX}/share/freem/doc/freem_history.*} (distributed in PostScript, PDF, and plain text formats).
  @section Production Readiness
  FreeM is not yet production-ready. There are several show-stopping bugs that preclude a general release for public use:
- Line 248  FreeM uses abbreviations for common lang
+ Line 252  FreeM uses abbreviations for common lang
  @table @asis
  @item @emph{$PREFIX}
  Refers to the base filesystem location within which FreeM is installed. For most distribution methods of FreeM, @emph{$PREFIX} represents either @code{/} or @code{/usr/local}.
+ @item @emph{dlabel}
+ Refers to a label in an M routine, beginning in the first column of the line. Can be a @emph{name} or an @emph{intlit}.
+ @item @emph{entryref}
+ Refers to an M routine entry point, denoted in the format @code{@emph{dlabel} [+@emph{intexpr}][^@emph{routine}]}.
  @item @emph{expr}
  Refers to any expression. Often presented in the format @emph{expr V <type>}, where @emph{V} means @emph{giving}; e.g., @emph{expr V lvn} means @emph{expression giving local variable name}.
  @item @emph{glvn}
- Line 256  Refers to the name of an M global, local
+ Line 264  Refers to the name of an M global, local
  Refers to the name of an M global variable.
  @item @emph{intexpr}
  Refers to an integer expression.
+ @item @emph{intlit}
+ Refers to an integer literal.
  @item @emph{ISV}, @emph{isv}
  Refers to an M intrinsic special variable; @code{$JOB} and @code{$IO} are examples of ISVs.
  @item @emph{L}
  Indicates a @emph{list} of the following item, e.g., @emph{L gvn} means @emph{list of global variable names}.
  @item @emph{lvn}
  Refers to the name of an M local variable.
+ @item @emph{strlit}
+ Refers to an M string literal.
  @item @emph{ssvn}
  Refers to the name of an M structured system variable.
  @item @emph{tvexpr}
  Refers to a truth-valued expression.
  @end table
+ @node A Note on Standards
+ @chapter A Note on Standards
+ @cindex MDC
+ @cindex M Development Committee
+ @cindex ANSI X11.1
+ @cindex standards, ANSI
+ @cindex standards, MDC
+ FreeM attempts to implement as many features as possible from the M Development Committee's unpublished @emph{Millennium Draft Standard}, as well as its predecessors.
+ The maintainer of FreeM (who is also the author of this book) is largely in favor of standardization efforts, and hopes that the MDC will resume activities, and will happily participate if it does so in an open, public, transparent, and democratic manner. Until then, however, FreeM will attempt to improve the M language, in cooperation with other free software M implementers where possible. Any breaking changes introduced in future MDC releases of the @emph{Standard} (such as the rumored @emph{M5}) which prove incompatible with FreeM will be handled via the @code{$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 673  Please note that FreeM is not entirely s
+ Line 699  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 895  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 $X
- Line 1992  Identical to @ref{$TRANSLATE()}, except
+ Line 2018  Identical to @ref{$TRANSLATE()}, except
  * AUNBLOCK::                            Decrement the block counter for one or more event classes.
  * BREAK::                               Interrupt a running routine to allow interactive debugging.
  * CLOSE::                               Close an input/output device.
- * CONST::                               Define a constant that cannot be altered after initial definition.
  * DO::                                  Transfer program control to one or more subroutines or introduces a new execution level.
  * ELSE::                                Execute the remainder of a line if @code{@ref{$TEST}} evaluates @emph{false}.
  * FOR::                                 Repeat execution of a line or block of code.
- Line 2005  Identical to @ref{$TRANSLATE()}, except
+ Line 2030  Identical to @ref{$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{$TRANSLATE()}, except
+ Line 2038  Identical to @ref{$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.
+ * ZCONST::                              Define a constant that cannot be altered after initial definition.
  * ZGO::                                 Unknown.
  * ZHALT::                               Unknown.
  * ZINSERT::                             Insert code into routine buffer.
- * ZJOB::                                Unknown.
+ * ZJOB::                                Invokes a 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::                               Quits multiple stack levels at once.
  * ZREMOVE::                             Remove code from routine buffer.
  * ZSAVE::                               Save routine buffer to disk.
+ * ZTHROW::                              Programmatically raise an error condition.
  * ZTRAP::                               Unknown.
+ * ZUNMAP::                              Remove a mapping of a global to a non-default namespace.
+ * ZWATCH::                              Enable or disable watchpoints, or set or clear watchpoints on specified globals, locals, or structured system variables.
+ * ZWITH::                               Set prefix for future variable references.
  * ZWRITE::                              Write local variable, global, or structured system variable to @code{@ref{$IO}}.
  @end menu
- Line 2333  In its argumentless form, @code{CLOSE} c
+ Line 2359  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 2405  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 2560  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 2705  If @code{LOCK} succeeds within @emph{tim
+ Line 2725  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{$TEST} until th
+ Line 2974  Saves the value of @code{$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 3038  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 3342  VIEW 133:@emph{tvexpr}
  @end table
- @node WATCH
- @section WATCH
- @cindex WATCH
- @cindex commands, WATCH
- @cindex commands, debugging
- @cindex commands, implementation-specific
- @cindex commands, non-standard
- @emph{FreeM Extension}
- Sets a watchpoint on a global, local, or SSVN node.
- @emph{Syntax}
- In its @emph{argumentless} form, @code{WATCH} toggles watchpoints on and off, provided the optional @emph{postcondition} is @emph{true} or omitted.
- @example
- WATCH[@emph{:postcondition}]
- @end example
- In its @emph{inclusive} form, @code{WATCH} adds, removes, or examines watchpoints, provided the optional @emph{postcondition} is @emph{true} or omitted.
- A @code{+} adds a new watchpoint to the following variable.
- A @code{-} removes an existing watchpoint for the following variable.
- A @code{?} examines the status of a watchpoint for the following variable.
- @example
- WATCH[@emph{:postcondition}] [+|-|?]@emph{var1}...,[+|-|?]@emph{varN}
- @end example
- The following example demonstrates turning watchpoint processing on and adding a watchpoint for global variable @code{^snw(1)}. It then changes the value of @code{^snw(1)}.
- @example
- DEFAULT.USER> WATCH
- Watchpoints enabled.
- DEFAULT.USER> WATCH +^SNW(1)
- Added '^SNW("1")' to the watchlist.
- DEFAULT.USER> SET ^SNW(1)="new value"
- >> WATCHPOINT:  ^SNW("1") => 'new value' (changed 1 times)
- @end example
- The following example will remove that watchpoint:
- @example
- DEFAULT.USER> WATCH -^SNW(1)
- Removed '^SNW("1")' from the watchlist.
- DEFAULT.USER> WATCH ?^SNW(1)
- '^SNW("1")' is not being watched.
- @end example
- @node WITH
- @section WITH
- @cindex WITH
- @cindex commands, WITH
- @cindex commands, non-standard
- @emph{FreeM Extension}
- NOTE: This command may be deprecated and removed in future FreeM releases.
- Sets a prefix to be applied to all subsequent local variable or constant references.
- @emph{Syntax}
- @example
- @code{WITH@emph{:postcondition} @emph{var-prefix}}
- @end example
- In the above single-argument form, sets the @code{$WITH} prefix to @emph{var-prefix}, provided that the optional @emph{postcondition} is either @emph{true} or omitted.
- The @emph{var-prefix} argument may be a string literal or any valid FreeM expression.
- @example
- @code{WITH@emph{:postcondition}}
- @end example
- In the above argumentless form, clears the @code{$WITH} prefix, provided the optional @emph{postcondition} is either @emph{true} or omitted. Equivalent to @code{WITH ""}.
  @node WRITE
- Line 3481  In the above argumentless form, clears t
+ Line 3363  In the above argumentless form, clears t
  @cindex commands, non-standard
  @emph{FreeM Extension}
+ @node ZCONST
+ @section ZCONST
+ @cindex ZCONST
+ @cindex commands, ZCONST
+ @cindex commands, non-standard
+ @emph{FreeM Extension}
+ Defines a local @emph{constant}, or variable that cannot be altered after its initial definition, provided the optional @emph{postcondition} is @emph{true} or omitted.
+ Constants must only be locals, and globals are not supported.
+ @emph{Syntax}
+ @example
+ @code{ZCONST@emph{:postcondition} @emph{mref1}=@emph{initial-value1},...,@emph{mrefN}=@emph{initial-valueN}}
+ @end example
  @node ZGO
  @section ZGO
  @cindex ZGO
- Line 3533  Loads routine @emph{<routine-name>} into
+ Line 3432  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 3506  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 3537  In its argumentless form, quits from @co
  @cindex commands, non-standard
  @emph{FreeM Extension}
+ @node ZUNMAP
+ @section ZUNMAP
+ @cindex ZUNMAP
+ @cindex commands, ZUNMAP
+ @cindex commands, implementation-specific
+ @cindex commands, non-standard
+ Removes any mapping connecting @emph{gvn} to a non-default namespace, provided the optional @emph{postcondition} evaluates to @emph{true} or is omitted.
+ @emph{Syntax}
+ @example
+ ZUNMAP GLOBAL @emph{gvn}
+ @end example
+ @node ZWATCH
+ @section ZWATCH
+ @cindex ZWATCH
+ @cindex commands, ZWATCH
+ @cindex commands, debugging
+ @cindex commands, implementation-specific
+ @cindex commands, non-standard
+ @emph{FreeM Extension}
+ Sets a watchpoint on a global, local, or SSVN node.
+ @emph{Syntax}
+ In its @emph{argumentless} form, @code{ZWATCH} toggles watchpoints on and off, provided the optional @emph{postcondition} is @emph{true} or omitted.
+ @example
+ ZWATCH[@emph{:postcondition}]
+ @end example
+ In its @emph{inclusive} form, @code{ZWATCH} adds, removes, or examines watchpoints, provided the optional @emph{postcondition} is @emph{true} or omitted.
+ A @code{+} adds a new watchpoint to the following variable.
+ A @code{-} removes an existing watchpoint for the following variable.
+ A @code{?} examines the status of a watchpoint for the following variable.
+ @example
+ ZWATCH[@emph{:postcondition}] [+|-|?]@emph{var1}...,[+|-|?]@emph{varN}
+ @end example
+ The following example demonstrates turning watchpoint processing on and adding a watchpoint for global variable @code{^snw(1)}. It then changes the value of @code{^snw(1)}.
+ @example
+ DEFAULT.USER> ZWATCH
+ Watchpoints enabled.
+ DEFAULT.USER> ZWATCH +^SNW(1)
+ Added '^SNW("1")' to the watchlist.
+ DEFAULT.USER> SET ^SNW(1)="new value"
+ >> WATCHPOINT:  ^SNW("1") => 'new value' (changed 1 times)
+ @end example
+ The following example will remove that watchpoint:
+ @example
+ DEFAULT.USER> ZWATCH -^SNW(1)
+ Removed '^SNW("1")' from the watchlist.
+ DEFAULT.USER> ZWATCH ?^SNW(1)
+ '^SNW("1")' is not being watched.
+ @end example
+ @node ZWITH
+ @section ZWITH
+ @cindex ZWITH
+ @cindex commands, ZWITH
+ @cindex commands, non-standard
+ @emph{FreeM Extension}
+ NOTE: This command may be deprecated and removed in future FreeM releases.
+ Sets a prefix to be applied to all subsequent local variable or constant references.
+ @emph{Syntax}
+ @example
+ @code{ZWITH@emph{:postcondition} @emph{var-prefix}}
+ @end example
+ In the above single-argument form, sets the @code{$WITH} prefix to @emph{var-prefix}, provided that the optional @emph{postcondition} is either @emph{true} or omitted.
+ The @emph{var-prefix} argument may be a string literal or any valid FreeM expression.
+ @example
+ @code{ZWITH@emph{:postcondition}}
+ @end example
+ In the above argumentless form, clears the @code{$WITH} prefix, provided the optional @emph{postcondition} is either @emph{true} or omitted. Equivalent to @code{ZWITH ""}.
  @node ZWRITE
  @section ZWRITE
  @cindex ZWRITE
- Line 4664  Transaction processing allows applicatio
+ Line 4712  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 4791  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 4789  The effect of this is that the operation
+ Line 4945  The effect of this is that the operation
  @cindex object-oriented programming
  @cindex programming, object-oriented
- @menu
- * Classes::                         The basis of object-oriented programming.
- * Inheritance::                     Basing one class upon another.
- * Methods::                         Attaching code to a class.
- * Public and Private Variables::    Managing class member access.
- * 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

FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>