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diff --git a/doc/NRE.3 b/doc/NRE.3 new file mode 100644 index 0000000..dfa6064 --- /dev/null +++ b/doc/NRE.3 @@ -0,0 +1,328 @@ +.\" +.\" Copyright (c) 2008 by Kevin B. Kenny. +.\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +.so man.macros +.TH NRE 3 8.6 Tcl "Tcl Library Procedures" +.BS +.SH NAME +Tcl_NRCreateCommand, Tcl_NRCallObjProc, Tcl_NREvalObj, Tcl_NREvalObjv, Tcl_NRCmdSwap, 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 +Interpreter in which to create or evaluate a command. +.AP char *cmdName in +Name of a new command to create. +.AP Tcl_ObjCmdProc *proc in +Implementation of a command that will be called whenever \fIcmdName\fR +is invoked as a command in the unoptimized way. +.AP Tcl_ObjCmdProc *nreProc in +Implementation of a command that will be called whenever \fIcmdName\fR +is invoked and requested to conserve the C stack. +.AP ClientData clientData in +Arbitrary one-word value that will be passed to \fIproc\fR, \fInreProc\fR, +\fIdeleteProc\fR and \fIobjProc\fR. +.AP Tcl_CmdDeleteProc *deleteProc in/out +Procedure to call before \fIcmdName\fR is deleted from the interpreter. +This procedure allows for command-specific cleanup. If \fIdeleteProc\fR +is \fBNULL\fR, then no procedure is called before the command is deleted. +.AP int objc in +Count of parameters provided to the implementation of a command. +.AP Tcl_Obj **objv in +Pointer to an array of Tcl objects. Each object holds the value of a +single word in the command to execute. +.AP Tcl_Obj *objPtr in +Pointer to a Tcl_Obj whose value is a script or expression to execute. +.AP int flags in +ORed combination of flag bits that specify additional options. +\fBTCL_EVAL_GLOBAL\fR is the only flag that is currently supported. +.\" TODO: This is a lie. But kbk didn't grasp TCL_EVAL_INVOKE and +.\" TCL_EVAL_NOERR well enough to document them. +.AP Tcl_Command cmd in +Token for a command that is to be used instead of the currently +executing command. +.AP Tcl_Obj *resultPtr out +Pointer to an unshared Tcl_Obj where the result of expression +evaluation is written. +.AP Tcl_NRPostProc *postProcPtr in +Pointer to a function that will be invoked when the command currently +executing in the interpreter designated by \fIinterp\fR completes. +.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 +This series of C functions provides an interface whereby commands that +are implemented in C can be evaluated, and invoke Tcl commands scripts +and scripts, without consuming space on the C stack. The non-recursive +evaluation is done by installing a \fItrampoline\fR, a small piece of +code that invokes a command or script, and then executes a series of +callbacks when the command or script returns. +.PP +The \fBTcl_NRCreateCommand\fR function creates a Tcl command in the +interpreter designated by \fIinterp\fR that is prepared to handle +nonrecursive evaluation with a trampoline. The \fIcmdName\fR argument +gives the name of the new command. If \fIcmdName\fR contains any +namespace qualifiers, then the new command is added to the specified +namespace; otherwise, it is added to the global namespace. \fIproc\fR +gives the procedure that will be called when the interpreter wishes to +evaluate the command in an unoptimized manner, and \fInreProc\fR is +the procedure that will be called when the interpreter wishes to +evaluate the command using a trampoline. \fIdeleteProc\fR is a +function that will be called before the command is deleted from the +interpreter. When any of the three functions is invoked, it is passed +the \fIclientData\fR parameter. +.PP +\fBTcl_NRCreateCommand\fR deletes any existing command +\fIname\fR already associated with the interpreter +(however see below for an exception where the existing command +is not deleted). +It returns a token that may be used to refer +to the command in subsequent calls to \fBTcl_GetCommandName\fR. +If \fBTcl_NRCreateCommand\fR is called for an interpreter that is in +the process of being deleted, then it does not create a new command, +does not delete any existing command of the same name, and returns NULL. +.PP +The \fIproc\fR and \fInreProc\fR function are expected to conform to +all the rules set forth for the \fIproc\fR argument to +\fBTcl_CreateObjCommand\fR(3) (\fIq.v.\fR). +.PP +When a command that is written to cope with evaluation via trampoline +is invoked without a trampoline on the stack, it will usually respond +to the invocation by creating a trampoline and calling the +trampoline-enabled implementation of the same command. This call is done by +means of \fBTcl_NRCallObjProc\fR. In the call to +\fBTcl_NRCallObjProc\fR, the \fIinterp\fR, \fIclientData\fR, +\fIobjc\fR and \fIobjv\fR parameters should be the same ones that were +passed to \fIproc\fR. The \fInreProc\fR parameter should designate the +trampoline-enabled implementation of the command. +.PP +\fBTcl_NREvalObj\fR arranges for the script contained in \fIobjPtr\fR +to be evaluated in the interpreter designated by \fIinterp\fR after +the current command (which must be trampoline-enabled) returns. It is +the method by which a command may invoke a script without consuming +space on the C stack. Similarly, \fBTcl_NREvalObjv\fR arranges to +invoke a single Tcl command whose words have already been separated +and substituted. The \fIobjc\fR and \fIobjv\fR parameters give the +words of the command to be evaluated when execution reaches the +trampoline. +.PP +\fBTcl_NRCmdSwap\fR allows for trampoline evaluation of a command whose +resolution is already known. The \fIcmd\fR parameter gives a +\fBTcl_Command\fR object (returned from \fBTcl_CreateObjCmd\fR or +\fBTcl_GetCommandFromObj\fR) identifying the command to be invoked in +the trampoline; this command must match the word in \fIobjv[0]\fR. +The remaining arguments are as for \fBTcl_NREvalObj\fR. +.PP +\fBTcl_NREvalObj\fR, \fBTcl_NREvalObjv\fR and \fBTcl_NRCmdSwap\fR +all accept a \fIflags\fR parameter, which is an OR-ed-together set of +bits to control evaluation. At the present time, the only supported flag +available to callers is \fBTCL_EVAL_GLOBAL\fR. +.\" TODO: Again, this is a lie. Do we want to explain TCL_EVAL_INVOKE +.\" and TCL_EVAL_NOERR? +If the \fBTCL_EVAL_GLOBAL\fR flag is set, the script or command is +evaluated in the global namespace. If it is not set, it is evaluated +in the current namespace. +.PP +\fBTcl_NRExprObj\fR arranges for the expression contained in \fIobjPtr\fR +to be evaluated in the interpreter designated by \fIinterp\fR after +the current command (which must be trampoline-enabled) returns. It is +the method by which a command may evaluate a Tcl expression without consuming +space on the C stack. The argument \fIresultPtr\fR is a pointer to an +unshared Tcl_Obj where the result of expression evaluation is to be written. +If expression evaluation returns any code other than TCL_OK, the +\fIresultPtr\fR value is left untouched. +.PP +All of the routines return \fBTCL_OK\fR if command or expression invocation +has been scheduled successfully. If for any reason the scheduling cannot +be completed (for example, if the interpreter is unable to find +the requested command), they return \fBTCL_ERROR\fR with an +appropriate message left in the interpreter's result. +.PP +\fBTcl_NRAddCallback\fR arranges to have a C function called when the +current trampoline-enabled command in the Tcl interpreter designated +by \fIinterp\fR returns. The \fIpostProcPtr\fR argument is a pointer +to the callback function, which must have arguments and return value +consistent with the \fBTcl_NRPostProc\fR data type: +.PP +.CS +typedef int +\fBTcl_NRPostProc\fR( + \fBClientData\fR \fIdata\fR[], + \fBTcl_Interp\fR *\fIinterp\fR, + int \fIresult\fR); +.CE +.PP +When the trampoline invokes the callback function, the \fIdata\fR +parameter will point to an array containing the four one-word +quantities that were passed to \fBTcl_NRAddCallback\fR in the +\fIdata0\fR through \fIdata3\fR parameters. The Tcl interpreter will +be designated by the \fIinterp\fR parameter, and the \fIresult\fR +parameter will contain the result (\fBTCL_OK\fR, \fBTCL_ERROR\fR, +\fBTCL_RETURN\fR, \fBTCL_BREAK\fR or \fBTCL_CONTINUE\fR) that was +returned by the command evaluation. The callback function is expected, +in turn, either to return a \fIresult\fR to control further evaluation. +.PP +Multiple \fBTcl_NRAddCallback\fR invocations may request multiple +callbacks, which may be to the same or different callback +functions. If multiple callbacks are requested, they are executed in +last-in, first-out order, that is, the most recently requested +callback is executed first. +.SH EXAMPLE +.PP +The usual pattern for Tcl commands that invoke other Tcl commands +is something like: +.PP +.CS +int +\fITheCmdObjProc\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", + \fITheCmdObjProc\fR, clientData, TheCmdDeleteProc); +.CE +.PP +To enable a command like this one for trampoline-based evaluation, +it must be split into three pieces: +.IP \(bu +A non-trampoline implementation, \fITheCmdNewObjProc\fR, +which will simply create a trampoline +and invoke the trampoline-based implementation. +.IP \(bu +A trampoline-enabled implementation, \fITheCmdNRObjProc\fR. This +function will perform the initialization, request that the trampoline +call the postprocessing routine after command evaluation, and finally, +request that the trampoline call the inner command. +.IP \(bu +A postprocessing routine, \fITheCmdPostProc\fR. This function will +perform the postprocessing formerly done after the return from the +inner command in \fITheCmdObjProc\fR. +.PP +The non-trampoline implementation is simple and stylized, containing +a single statement: +.PP +.CS +int +\fITheCmdNewObjProc\fR( + ClientData clientData, + Tcl_Interp *interp, + int objc, + Tcl_Obj *const objv[]) +{ + return \fBTcl_NRCallObjProc\fR(interp, name, + \fITheCmdNRObjProc\fR, clientData, objc, objv); +} +.CE +.PP +The trampoline-enabled implementation requests postprocessing, +and returns to the trampoline requesting command evaluation. +.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 +The postprocessing procedure does whatever the original command did +upon return from the inner evaluation. +.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_NREvalObj\fR */ + + \fI... postprocessing ...\fR + + return result; +} +.CE +.PP +If \fItheCommand\fR is a command that results in multiple commands or +scripts being evaluated, its postprocessing routine may schedule +additional postprocessing and then request another command evaluation +by means of \fBTcl_NREvalObj\fR or one of the other evaluation +routines. Looping and sequencing constructs may be implemented in this way. +.PP +Finally, to install a trampoline-enabled command in the interpreter, +\fBTcl_NRCreateCommand\fR is used in place of +\fBTcl_CreateObjCommand\fR. It accepts two command procedures instead +of one. The first is for use when no trampoline is yet on the stack, +and the second is for use when there is already a trampoline in place. +.PP +.CS +\fBTcl_NRCreateCommand\fR(interp, "theCommand", + \fITheCmdObjProc\fR, \fITheCmdNRObjProc\fR, clientData, + TheCmdDeleteProc); +.CE +.SH "SEE ALSO" +Tcl_CreateCommand(3), Tcl_CreateObjCommand(3), Tcl_EvalObjEx(3), Tcl_GetCommandFromObj(3), Tcl_ExprObj(3) +.SH KEYWORDS +stackless, nonrecursive, execute, command, global, object, result, script +.SH COPYRIGHT +Copyright (c) 2008 by Kevin B. Kenny |