.\"
.\" Copyright (c) 2008 Kevin B. Kenny.
.\" Copyright (c) 2018 Nathan Coulter.
.\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH NRE 3tcl 8.6 Tcl "Tcl Library Procedures"
.\" 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?
.\"	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 ?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
.\}
.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
'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
.RS
.nf
.ta .25i .5i .75i 1i
..
.\"	# CE - end code excerpt
.de CE
.fi
.RE
..
.\"	# 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
.SH NAME
Tcl_NRCreateCommand, Tcl_NRCallObjProc, Tcl_NREvalObj, Tcl_NREvalObjv, Tcl_NRCmdSwap, Tcl_NRExprObj, Tcl_NRAddCallback \- Non-Recursive (stackless) evaluation of Tcl scripts.
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
Tcl_Command
\fBTcl_NRCreateCommand\fR(\fIinterp, cmdName, proc, nreProc, clientData,
                    deleteProc\fR)
.sp
int
\fBTcl_NRCallObjProc\fR(\fIinterp, nreProc, clientData, objc, objv\fR)
.sp
int
\fBTcl_NREvalObj\fR(\fIinterp, objPtr, flags\fR)
.sp
int
\fBTcl_NREvalObjv\fR(\fIinterp, objc, objv, flags\fR)
.sp
int
\fBTcl_NRCmdSwap\fR(\fIinterp, cmd, objc, objv, flags\fR)
.sp
int
\fBTcl_NRExprObj\fR(\fIinterp, objPtr, resultPtr\fR)
.sp
void
\fBTcl_NRAddCallback\fR(\fIinterp, postProcPtr, data0, data1, data2, data3\fR)
.fi
.SH ARGUMENTS
.AS Tcl_CmdDeleteProc *interp in
.AP Tcl_Interp *interp in
The relevant Interpreter.
.AP "const char" *cmdName in
Name of the command to create.
.AP Tcl_ObjCmdProc *proc in
Called in order to evaluate a command.  Is often just a small wrapper that uses
\fBTcl_NRCallObjProc\fR to call \fInreProc\fR using a new trampoline.  Behaves
in the same way as the \fIproc\fR argument to \fBTcl_CreateObjCommand\fR(3tcl)
(\fIq.v.\fR).
.AP Tcl_ObjCmdProc *nreProc in
Called instead of \fIproc\fR when a trampoline is already in use.
.AP ClientData clientData in
Arbitrary one-word value passed to \fIproc\fR, \fInreProc\fR, \fIdeleteProc\fR
and \fIobjProc\fR.
.AP Tcl_CmdDeleteProc *deleteProc in/out
Called before \fIcmdName\fR is deleted from the interpreter, allowing for
command-specific cleanup. May be NULL.
.AP int objc in
Number of items in \fIobjv\fR.
.AP Tcl_Obj **objv in
Words in the command.
.AP Tcl_Obj *objPtr in
A script or expression to evaluate.
.AP int flags in
As described for \fITcl_EvalObjv\fR.
.PP
.AP Tcl_Command cmd in
Token to use instead of one derived from the first word of \fIobjv\fR in order
to evaluate a command.
.AP Tcl_Obj *resultPtr out
Pointer to an unshared Tcl_Obj where the result of the evaluation is stored if
the return code is TCL_OK.
.AP Tcl_NRPostProc *postProcPtr in
A function to push.
.AP ClientData data0 in
.AP ClientData data1 in
.AP ClientData data2 in
.AP ClientData data3 in
\fIdata0\fR through \fIdata3\fR are four one-word values that will be passed
to the function designated by \fIpostProcPtr\fR when it is invoked.
.BE
.SH DESCRIPTION
.PP
These functions provide an interface to the function stack that an interpreter
iterates through to evaluate commands.  The routine behind a command is
implemented by an initial function and any additional functions that the
routine pushes onto the stack as it progresses.  The interpreter itself pushes
functions onto the stack to react to the end of a routine and to exercise other
forms of control such as switching between in-progress stacks and the
evaluation of other scripts at additional levels without adding frames to the C
stack.  To execute a routine, the initial function for the routine is called
and then a small bit of code called a \fItrampoline\fR iteratively takes
functions off the stack and calls them, using the value of the last call as the
value of the routine.
.PP
\fBTcl_NRCallObjProc\fR calls \fInreProc\fR using a new trampoline.
.PP
\fBTcl_NRCreateCommand\fR, an alternative to \fBTcl_CreateObjCommand\fR,
resolves \fIcmdName\fR, which may contain namespace qualifiers, relative to the
current namespace, creates a command by that name, and returns a token for the
command which may be used in subsequent calls to \fBTcl_GetCommandName\fR.
Except for a few cases noted below any existing command by the same name is
first deleted.  If \fIinterp\fR is in the process of being deleted
\fBTcl_NRCreateCommand\fR does not create any command, does not delete any
command, and returns NULL.
.PP
\fBTcl_NREvalObj\fR pushes a function that is like \fBTcl_EvalObjEx\fR but
consumes no space on the C stack.
.PP
\fBTcl_NREvalObjv\fR pushes a function that is like \fBTcl_EvalObjv\fR but
consumes no space on the C stack.
.PP
\fBTcl_NRCmdSwap\fR is like \fBTcl_NREvalObjv\fR, but uses \fIcmd\fR, a token
previously returned by \fBTcl_CreateObjCommand\fR or
\fBTcl_GetCommandFromObj\fR, instead of resolving the first word of \fIobjv\fR.
.  The name of this command must be the same as \fIobjv[0]\fR.
.PP
\fBTcl_NRExprObj\fR pushes a function that evaluates \fIobjPtr\fR as an
expression in the same manner as \fBTcl_ExprObj\fR but without consuming space
on the C stack.
.PP
All of the functions return \fBTCL_OK\fR if the evaluation of the script,
command, or expression has been scheduled successfully.  Otherwise (for example
if the command name cannot be resolved), they return \fBTCL_ERROR\fR and store
a message as the interpreter's result.
.PP
\fBTcl_NRAddCallback\fR pushes \fIpostProcPtr\fR.  The signature for
\fBTcl_NRPostProc\fR is:
.PP
.CS
typedef int
\fBTcl_NRPostProc\fR(
        \fBClientData\fR \fIdata\fR[],
        \fBTcl_Interp\fR *\fIinterp\fR,
        int \fIresult\fR);
.CE
.PP
\fIdata\fR is a pointer to an array containing \fIdata0\fR through \fIdata3\fR.
\fIresult\fR is the value returned by the previous function implementing part
the routine.
.SH EXAMPLE
.PP
The following command uses \fBTcl_EvalObjEx\fR, which consumes space on the C
stack, to evalute a script:
.PP
.CS
int
\fITheCmdOldObjProc\fR(
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,
    Tcl_Obj *const objv[])
{
    int result;
    Tcl_Obj *objPtr;

    \fI... preparation ...\fR

    result = \fBTcl_EvalObjEx\fR(interp, objPtr, 0);

    \fI... postprocessing ...\fR

    return result;
}
\fBTcl_CreateObjCommand\fR(interp, "theCommand",
        \fITheCmdOldObjProc\fR, clientData, TheCmdDeleteProc);
.CE
.PP
To avoid consuming space on the C stack, \fITheCmdOldObjProc\fR is renamed to
\fITheCmdNRObjProc\fR and the postprocessing step is split into a separate
function, \fITheCmdPostProc\fR, which is pushed onto the function stack.
\fITcl_EvalObjEx\fR is replaced with \fITcl_NREvalObj\fR, which uses a
trampoline instead of consuming space on the C stack.  A new version of
\fITheCmdOldObjProc\fR is just a a wrapper that uses \fBTcl_NRCallObjProc\fR to
call \fITheCmdNRObjProc\fR:
.PP
.CS
int
\fITheCmdOldObjProc\fR(
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,
    Tcl_Obj *const objv[])
{
    return \fBTcl_NRCallObjProc\fR(interp, \fITheCmdNRObjProc\fR,
            clientData, objc, objv);
}
.CE
.PP
.CS
int
\fITheCmdNRObjProc\fR
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,
    Tcl_Obj *const objv[])
{
    Tcl_Obj *objPtr;

    \fI... preparation ...\fR

    \fBTcl_NRAddCallback\fR(interp, \fITheCmdPostProc\fR,
            data0, data1, data2, data3);
    /* \fIdata0 .. data3\fR are up to four one-word items to
     * pass to the postprocessing procedure */

    return \fBTcl_NREvalObj\fR(interp, objPtr, 0);
}
.CE
.PP
.CS
int
\fITheCmdNRPostProc\fR(
    ClientData data[],
    Tcl_Interp *interp,
    int result)
{
    /* \fIdata[0] .. data[3]\fR are the four words of data
     * passed to \fBTcl_NRAddCallback\fR */

    \fI... postprocessing ...\fR

    return result;
}
.CE
.PP
Any function comprising a routine can push other functions, making it possible
implement looping and sequencing constructs using the function stack.
.PP
.SH "REFERENCE COUNT MANAGEMENT"
.PP
The first \fIobjc\fR values in the \fIobjv\fR array passed to the functions
\fBTcl_NRCallObjProc\fR, \fBTcl_NREvalObjv\fR, and \fBTcl_NRCmdSwap\fR should
have a reference count of at least 1; they may have additional references
taken during the execution.
.PP
The \fIobjPtr\fR argument to \fBTcl_NREvalObj\fR and \fBTcl_NRExprObj\fR
should have a reference count of at least 1, and may have additional
references taken to it during execution.
.PP
The \fIresultObj\fR argument to \fBTcl_NRExprObj\fR should be an unshared
object.
.PP
Use \fBTcl_NRAddCallback\fR to schedule any required final decrementing of the
reference counts of arguments to any of the other functions on this page, as
with any other post-processing step in the non-recursive execution engine.
.PP
The
.SH "SEE ALSO"
Tcl_CreateCommand(3tcl), Tcl_CreateObjCommand(3tcl), Tcl_EvalObjEx(3tcl), Tcl_GetCommandFromObj(3tcl), Tcl_ExprObj(3tcl)
.SH KEYWORDS
stackless, nonrecursive, execute, command, global, value, result, script
.SH COPYRIGHT
Copyright \(co 2008 Kevin B. Kenny.
Copyright \(co 2018 Nathan Coulter.