'\"
'\" Copyright (c) 2006 Miguel Sofer
'\" Copyright (c) 2006 Donal K. Fellows
'\"
.\" 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)
.\"
.\" .AS ?type? ?name?
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.\"	name are examples of largest possible arguments that will be passed
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.\" .VS ?version? ?br?
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.\"	of man pages.  The first argument is ignored and used for recording
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.\"	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.
.\"
.\" .UL arg1 arg2
.\"	Print arg1 underlined, then print arg2 normally.
.\"
.\" .QW arg1 ?arg2?
.\"	Print arg1 in quotes, then arg2 normally (for trailing punctuation).
.\"
.\" .PQ arg1 ?arg2?
.\"	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
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\&\\fI\\$1\\fP
.\}
.\}
..
.\"	# define tabbing values for .AP
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.nr )A 10n
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.\"
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.nr )C \\n()Bu+\\w'(in/out)'u+2n
..
.AS Tcl_Interp Tcl_CreateInterp in/out
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.if n \l'\\n(.lu\(ul'
.if n .fi
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.de BE
.nf
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.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'
.\}
.\}
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'ti 0
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.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
.\}
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.\"	# DS - begin display
.de DS
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.nf
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..
.\"	# DE - end display
.de DE
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.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
..
.\"	# CS - begin code excerpt
.de CS
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.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 ""
..
.TH apply n "" Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
apply \- Apply an anonymous function
.SH SYNOPSIS
\fBapply \fIfunc\fR ?\fIarg1 arg2 ...\fR?
.BE
.SH DESCRIPTION
.PP
The command \fBapply\fR applies the function \fIfunc\fR to the arguments
\fIarg1 arg2 ...\fR and returns the result. 
.PP
The function \fIfunc\fR is a two element list \fI{args body}\fR or a three
element list \fI{args body namespace}\fR (as if the
\fBlist\fR command had been used). 
The first element \fIargs\fR specifies the formal arguments to
\fIfunc\fR. The specification of the formal arguments \fIargs\fR
is shared with the \fBproc\fR command, and is described in detail in the
corresponding manual page.
.PP
The contents of \fIbody\fR are executed by the Tcl interpreter
after the local variables corresponding to the formal arguments are given
the values of the actual parameters \fIarg1 arg2 ...\fR.
When \fIbody\fR is being executed, variable names normally refer to
local variables, which are created automatically when referenced and
deleted when \fBapply\fR returns.  One local variable is automatically
created for each of the function's arguments.
Global variables can only be accessed by invoking
the \fBglobal\fR command or the \fBupvar\fR command.
Namespace variables can only be accessed by invoking
the \fBvariable\fR command or the \fBupvar\fR command.
.PP
The invocation of \fBapply\fR adds a call frame to Tcl's evaluation stack
(the stack of frames accessed via \fBuplevel\fR). The execution of \fIbody\fR
proceeds in this call frame, in the namespace given by \fInamespace\fR or
in the global namespace if none was specified. If given, \fInamespace\fR is
interpreted relative to the global namespace even if its name does not start
with
.QW :: .
.PP
The semantics of \fBapply\fR can also be described by:
.PP
.CS
proc apply {fun args} {
   set len [llength $fun]
   if {($len < 2) || ($len > 3)} {
      error "can't interpret \e"$fun\e" as anonymous function"
   }
   lassign $fun argList body ns
   set name ::$ns::[getGloballyUniqueName]
   set body0 {
      rename [lindex [info level 0] 0] {}
   }
   proc $name $argList ${body0}$body
   set code [catch {uplevel 1 $name $args} res opt]
   return -options $opt $res
}
.CE
.SH EXAMPLES
This shows how to make a simple general command that applies a transformation
to each element of a list.
.CS
proc map {lambda list} {
   set result {}
   foreach item $list {
      lappend result [\fBapply\fR $lambda $item]
   }
   return $result
}
map {x {return [string length $x]:$x}} {a bb ccc dddd}
      \fI\(-> 1:a 2:bb 3:ccc 4:dddd\fR
map {x {expr {$x**2 + 3*$x - 2}}} {-4 -3 -2 -1 0 1 2 3 4}
      \fI\(-> 2 -2 -4 -4 -2 2 8 16 26\fR
.CE
.PP
The \fBapply\fR command is also useful for defining callbacks for use in the
\fBtrace\fR command:
.CS
set vbl "123abc"
trace add variable vbl write {\fBapply\fR {{v1 v2 op} {
   upvar 1 $v1 v
   puts "updated variable to \e"$v\e""
}}}
set vbl 123
set vbl abc
.CE
.SH "SEE ALSO"
proc(n), uplevel(n)
.SH KEYWORDS
argument, procedure, anonymous function