'\"
'\" Copyright (c) 2001 by Kevin B. Kenny.  All rights reserved.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
'\" RCS: @(#) $Id: lset.n,v 1.6 2003/01/23 14:18:33 dkf Exp $
'\" 
'\" The definitions below are for supplemental macros used in Tcl/Tk
'\" manual entries.
'\"
'\" .AP type name in/out ?indent?
'\"	Start paragraph describing an argument to a library procedure.
'\"	type is type of argument (int, etc.), in/out is either "in", "out",
'\"	or "in/out" to describe whether procedure reads or modifies arg,
'\"	and indent is equivalent to second arg of .IP (shouldn't ever be
'\"	needed;  use .AS below instead)
'\"
'\" .AS ?type? ?name?
'\"	Give maximum sizes of arguments for setting tab stops.  Type and
'\"	name are examples of largest possible arguments that will be passed
'\"	to .AP later.  If args are omitted, default tab stops are used.
'\"
'\" .BS
'\"	Start box enclosure.  From here until next .BE, everything will be
'\"	enclosed in one large box.
'\"
'\" .BE
'\"	End of box enclosure.
'\"
'\" .CS
'\"	Begin code excerpt.
'\"
'\" .CE
'\"	End code excerpt.
'\"
'\" .VS ?version? ?br?
'\"	Begin vertical sidebar, for use in marking newly-changed parts
'\"	of man pages.  The first argument is ignored and used for recording
'\"	the version when the .VS was added, so that the sidebars can be
'\"	found and removed when they reach a certain age.  If another argument
'\"	is present, then a line break is forced before starting the sidebar.
'\"
'\" .VE
'\"	End of vertical sidebar.
'\"
'\" .DS
'\"	Begin an indented unfilled display.
'\"
'\" .DE
'\"	End of indented unfilled display.
'\"
'\" .SO
'\"	Start of list of standard options for a Tk widget.  The
'\"	options follow on successive lines, in four columns separated
'\"	by tabs.
'\"
'\" .SE
'\"	End of list of standard options for a Tk widget.
'\"
'\" .OP cmdName dbName dbClass
'\"	Start of description of a specific option.  cmdName gives the
'\"	option's name as specified in the class command, dbName gives
'\"	the option's name in the option database, and dbClass gives
'\"	the option's class in the option database.
'\"
'\" .UL arg1 arg2
'\"	Print arg1 underlined, then print arg2 normally.
'\"
'\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $
'\"
'\"	# Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
.if t .wh -1.3i ^B
.nr ^l \n(.l
.ad b
'\"	# Start an argument description
.de AP
.ie !"\\$4"" .TP \\$4
.el \{\
.   ie !"\\$2"" .TP \\n()Cu
.   el          .TP 15
.\}
.ta \\n()Au \\n()Bu
.ie !"\\$3"" \{\
\&\\$1	\\fI\\$2\\fP	(\\$3)
.\".b
.\}
.el \{\
.br
.ie !"\\$2"" \{\
\&\\$1	\\fI\\$2\\fP
.\}
.el \{\
\&\\fI\\$1\\fP
.\}
.\}
..
'\"	# define tabbing values for .AP
.de AS
.nr )A 10n
.if !"\\$1"" .nr )A \\w'\\$1'u+3n
.nr )B \\n()Au+15n
.\"
.if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n
.nr )C \\n()Bu+\\w'(in/out)'u+2n
..
.AS Tcl_Interp Tcl_CreateInterp in/out
'\"	# BS - start boxed text
'\"	# ^y = starting y location
'\"	# ^b = 1
.de BS
.br
.mk ^y
.nr ^b 1u
.if n .nf
.if n .ti 0
.if n \l'\\n(.lu\(ul'
.if n .fi
..
'\"	# BE - end boxed text (draw box now)
.de BE
.nf
.ti 0
.mk ^t
.ie n \l'\\n(^lu\(ul'
.el \{\
.\"	Draw four-sided box normally, but don't draw top of
.\"	box if the box started on an earlier page.
.ie !\\n(^b-1 \{\
\h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
.\}
.el \}\
\h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
.\}
.\}
.fi
.br
.nr ^b 0
..
'\"	# VS - start vertical sidebar
'\"	# ^Y = starting y location
'\"	# ^v = 1 (for troff;  for nroff this doesn't matter)
.de VS
.if !"\\$2"" .br
.mk ^Y
.ie n 'mc \s12\(br\s0
.el .nr ^v 1u
..
'\"	# VE - end of vertical sidebar
.de VE
.ie n 'mc
.el \{\
.ev 2
.nf
.ti 0
.mk ^t
\h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n'
.sp -1
.fi
.ev
.\}
.nr ^v 0
..
'\"	# Special macro to handle page bottom:  finish off current
'\"	# box/sidebar if in box/sidebar mode, then invoked standard
'\"	# page bottom macro.
.de ^B
.ev 2
'ti 0
'nf
.mk ^t
.if \\n(^b \{\
.\"	Draw three-sided box if this is the box's first page,
.\"	draw two sides but no top otherwise.
.ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
.el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
.\}
.if \\n(^v \{\
.nr ^x \\n(^tu+1v-\\n(^Yu
\kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c
.\}
.bp
'fi
.ev
.if \\n(^b \{\
.mk ^y
.nr ^b 2
.\}
.if \\n(^v \{\
.mk ^Y
.\}
..
'\"	# DS - begin display
.de DS
.RS
.nf
.sp
..
'\"	# DE - end display
.de DE
.fi
.RE
.sp
..
'\"	# SO - start of list of standard options
.de SO
.SH "STANDARD OPTIONS"
.LP
.nf
.ta 5.5c 11c
.ft B
..
'\"	# SE - end of list of standard options
.de SE
.fi
.ft R
.LP
See the \\fBoptions\\fR manual entry for details on the standard options.
..
'\"	# OP - start of full description for a single option
.de OP
.LP
.nf
.ta 4c
Command-Line Name:	\\fB\\$1\\fR
Database Name:	\\fB\\$2\\fR
Database Class:	\\fB\\$3\\fR
.fi
.IP
..
'\"	# CS - begin code excerpt
.de CS
.RS
.nf
.ta .25i .5i .75i 1i
..
'\"	# CE - end code excerpt
.de CE
.fi
.RE
..
.de UL
\\$1\l'|0\(ul'\\$2
..
.TH lset n 8.4 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
lset \- Change an element in a list
.SH SYNOPSIS
\fBlset \fIvarName ?index...? newValue\fR
.BE
.SH DESCRIPTION
.PP
The \fBlset\fR command accepts a parameter, \fIvarName\fR, which
it interprets as the name of a variable containing a Tcl list. 
It also accepts zero or more \fIindices\fR into
the list.  The indices may be presented either consecutively on the
command line, or grouped in a
Tcl list and presented as a single argument.
Finally, it accepts a new value for an element of \fIvarName\fR.
.PP
If no indices are presented, the command takes the form:
.CS
lset varName newValue
.CE
or
.CS
lset varName {} newValue
.CE
In this case, \fInewValue\fR replaces the old value of the variable
\fIvarName\fR.
.PP
When presented with a single index, the \fBlset\fR command
treats the content of the \fIvarBane\fR variable as a Tcl list.
It addresses the \fIindex\fR'th element in it 
(0 refers to the first element of the list).
When interpreting the list, \fBlset\fR observes the same rules
concerning braces and quotes and backslashes as the Tcl command
interpreter; however, variable
substitution and command substitution do not occur.
The command constructs a new list in which the designated element is
replaced with \fInewValue\fR.  This new list is stored in the
variable \fIvarName\fR, and is also the return value from the \fBlset\fR
command.
.PP
If \fIindex\fR is negative or greater than or equal to the number
of elements in \fI$varName\fR, then an error occurs.
.PP
If \fIindex\fR has the value \fBend\fR, it refers to the last element
in the list, and \fBend\-\fIinteger\fR refers to the last element in
the list minus the specified integer offset.
.PP
If additional \fIindex\fR arguments are supplied, then each argument is
used in turn to address an element within a sublist designated
by the previous indexing operation,
allowing the script to alter elements in sublists.  The command,
.CS
lset a 1 2 newValue
.CE
or
.CS
lset a {1 2} newValue
.CE
replaces element 2 of sublist 1 with \fInewValue\fR.
.PP
The integer appearing in each \fIindex\fR argument must be greater
than or equal to zero.  The integer appearing in each \fIindex\fR
argument must be strictly less than the length of the corresponding
list.  In other words, the \fBlset\fR command cannot change the size
of a list.  If an index is outside the permitted range, an error is reported.
.SH EXAMPLES
In each of these examples, the initial value of \fIx\fR is:
.CS
set x [list [list a b c] [list d e f] [list g h i]]
  => {a b c} {d e f} {g h i}
.CE
The indicated return value also becomes the new value of \fIx\fR
(except in the last case, which is an error which leaves the value of
\fIx\fR unchanged.)
.CS
lset x {j k l} => j k l
lset x {} {j k l} => j k l
lset x 0 j => j {d e f} {g h i}
lset x 2 j => {a b c} {d e f} j
lset x end j => {a b c} {d e f} j
lset x end-1 j => {a b c} j {g h i}
lset x 2 1 j => {a b c} {d e f} {g j i}
lset x {2 1} j => {a b c} {d e f} {g j i}
lset x {2 3} j => \fIlist index out of range\fR
.CE
In the following examples, the initial value of \fIx\fR is:
.CS
set x [list [list [list a b] [list c d]] \e
            [list [list e f] [list g h]]]
 => {{a b} {c d}} {{e f} {g h}}
.CE
The indicated return value also becomes the new value of \fIx\fR.
.CS
lset x 1 1 0 j => {{a b} {c d}} {{e f} {j h}}
lset x {1 1 0} j => {{a b} {c d}} {{e f} {j h}}
.CE
.SH "SEE ALSO"
list(n), lappend(n), lindex(n), linsert(n), llength(n), lsearch(n), 
lsort(n), lrange(n), lreplace(n)

.SH KEYWORDS
element, index, list, replace, set
