'\"
'\" Copyright (c) 2018 Peter Spjuth.  All rights reserved.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH lpop 3tcl 8.7 Tcl "Tcl Built-In Commands"
.\" The -*- nroff -*- 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)
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.\"	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.
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.\" .SO ?manpage?
.\"	Start of list of standard options for a Tk widget. The manpage
.\"	argument defines where to look up the standard options; if
.\"	omitted, defaults to "options". The options follow on successive
.\"	lines, in three 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.
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.\" .UL arg1 arg2
.\"	Print arg1 underlined, then print arg2 normally.
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.\" .QW arg1 ?arg2?
.\"	Print arg1 in quotes, then arg2 normally (for trailing punctuation).
.\"
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.\"	Print an open parenthesis, arg1 in quotes, then arg2 normally
.\"	(for trailing punctuation) and then a closing parenthesis.
.\"
.\"	# 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
..
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.\"	# ^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
..
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.de VE
.ie n 'mc
.el \{\
.ev 2
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.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
.\}
..
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.de DS
.RS
.nf
.sp
..
.\"	# DE - end display
.de DE
.fi
.RE
.sp
..
.\"	# SO - start of list of standard options
.de SO
'ie '\\$1'' .ds So \\fBoptions\\fR
'el .ds So \\fB\\$1\\fR
.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 \\*(So 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
..
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.de CS
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.nf
.ta .25i .5i .75i 1i
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.de CE
.fi
.RE
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.\"	# UL - underline word
.de UL
\\$1\l'|0\(ul'\\$2
..
.\"	# QW - apply quotation marks to word
.de QW
.ie '\\*(lq'"' ``\\$1''\\$2
.\"" fix emacs highlighting
.el \\*(lq\\$1\\*(rq\\$2
..
.\"	# PQ - apply parens and quotation marks to word
.de PQ
.ie '\\*(lq'"' (``\\$1''\\$2)\\$3
.\"" fix emacs highlighting
.el (\\*(lq\\$1\\*(rq\\$2)\\$3
..
.\"	# QR - quoted range
.de QR
.ie '\\*(lq'"' ``\\$1''\\-``\\$2''\\$3
.\"" fix emacs highlighting
.el \\*(lq\\$1\\*(rq\\-\\*(lq\\$2\\*(rq\\$3
..
.\"	# MT - "empty" string
.de MT
.QW ""
..
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
lpop \- Get and remove an element in a list
.SH SYNOPSIS
\fBlpop \fIvarName ?index ...?\fR
.BE
.SH DESCRIPTION
.PP
The \fBlpop\fR command accepts a parameter, \fIvarName\fR, which
it interprets as the name of a variable containing a Tcl list.
It also accepts one or more \fIindices\fR into
the list. If no indices are presented, it defaults to "end".
.PP
When presented with a single index, the \fBlpop\fR command
addresses the \fIindex\fR'th element in it, removes if from the list
and returns the element.
.PP
If \fIindex\fR is negative or greater or equal than the number
of elements in \fI$varName\fR, then an error occurs.
.PP
The interpretation of each simple \fIindex\fR value is the same as
for the command \fBstring index\fR, supporting simple index
arithmetic and indices relative to the end of the list.
.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 remove elements in sublists.
The command,
.PP
.CS
\fBlpop\fR a 1 2
.CE
.PP
gets and removes element 2 of sublist 1.
.PP
.SH EXAMPLES
.PP
In each of these examples, the initial value of \fIx\fR is:
.PP
.CS
set x [list [list a b c] [list d e f] [list g h i]]
      \fI\(-> {a b c} {d e f} {g h i}\fR
.CE
.PP
The indicated value becomes the new value of \fIx\fR
(except in the last case, which is an error which leaves the value of
\fIx\fR unchanged.)
.PP
.CS
\fBlpop\fR x 0
      \fI\(-> {d e f} {g h i}\fR
\fBlpop\fR x 2
      \fI\(-> {a b c} {d e f}\fR
\fBlpop\fR x end
      \fI\(-> {a b c} {d e f}\fR
\fBlpop\fR x end-1
      \fI\(-> {a b c} {g h i}\fR
\fBlpop\fR x 2 1
      \fI\(-> {a b c} {d e f} {g i}\fR
\fBlpop\fR x 2 3 j
      \fI\(-> list index out of range\fR
.CE
.PP
In the following examples, the initial value of \fIx\fR is:
.PP
.CS
set x [list [list [list a b] [list c d]] \e
            [list [list e f] [list g h]]]
      \fI\(-> {{a b} {c d}} {{e f} {g h}}\fR
.CE
.PP
The indicated value becomes the new value of \fIx\fR.
.PP
.CS
\fBlpop\fR x 1 1 0
      \fI\(-> {{a b} {c d}} {{e f} h}\fR
.CE
.SH "SEE ALSO"
list(3tcl), lappend(3tcl), lassign(3tcl), lindex(3tcl), linsert(3tcl), llength(3tcl),
lmap(3tcl), lrange(3tcl), lremove(3tcl), lrepeat(3tcl), lreplace(3tcl),
lreverse(3tcl), lsearch(3tcl), lset(3tcl), lsort(3tcl),
string(3tcl)
.SH KEYWORDS
element, index, list, remove, pop, stack, queue
'\"Local Variables:
'\"mode: nroff
'\"End: