Tcl Documentation > Tcl C API > NRE

Tcl Applications | Tcl Commands | Tcl C API

NAME

Tcl_NRCreateCommand, Tcl_NRCallObjProc, Tcl_NREvalObj, Tcl_NREvalObjv, Tcl_NRCmdSwap, Tcl_NRExprObj, Tcl_NRAddCallback — Non-Recursive (stackless) evaluation of Tcl scripts.

SYNOPSIS

#include <tcl.h>

Tcl_Command

Tcl_NRCreateCommand(interp, cmdName, proc, nreProc, clientData,

deleteProc)

int

Tcl_NRCallObjProc(interp, nreProc, clientData, objc, objv)

int

Tcl_NREvalObj(interp, objPtr, flags)

int

Tcl_NREvalObjv(interp, objc, objv, flags)

int

Tcl_NRCmdSwap(interp, cmd, objc, objv, flags)

int

Tcl_NRExprObj(interp, objPtr, resultPtr)

void

Tcl_NRAddCallback(interp, postProcPtr, data0, data1, data2, data3)

ARGUMENTS

DESCRIPTION

EXAMPLE

SEE ALSO

KEYWORDS

COPYRIGHT

NAME

SYNOPSIS

ARGUMENTS

Tcl_Interp *interp (in)

The relevant Interpreter.

char *cmdName (in)

Name of the command to create.

Tcl_ObjCmdProc *proc (in)

Called in order to evaluate a command. Is often just a small wrapper that uses Tcl_NRCallObjProc to call nreProc using a new trampoline. Behaves in the same way as the proc argument to Tcl_CreateObjCommand(3) (q.v.).

Tcl_ObjCmdProc *nreProc (in)

Called instead of proc when a trampoline is already in use.

ClientData clientData (in)

Arbitrary one-word value passed to proc, nreProc, deleteProc and objProc.

Tcl_CmdDeleteProc *deleteProc (in/out)

Called before cmdName is deleted from the interpreter, allowing for command-specific cleanup. May be NULL.

int objc (in)

Number of items in objv.

Tcl_Obj **objv (in)

Words in the command.

Tcl_Obj *objPtr (in)

A script or expression to evaluate.

int flags (in)

As described for Tcl_EvalObjv.

Tcl_Command cmd (in)

Token to use instead of one derived from the first word of objv in order to evaluate a command.

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.

Tcl_NRPostProc *postProcPtr (in)

A function to push.

ClientData data0 (in)

ClientData data1 (in)

ClientData data2 (in)

ClientData data3 (in)

data0 through data3 are four one-word values that will be passed to the function designated by postProcPtr when it is invoked.

DESCRIPTION

Tcl_NRCallObjProc calls nreProc using a new trampoline.

Tcl_NRCreateCommand, an alternative to Tcl_CreateObjCommand, resolves cmdName, 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 Tcl_GetCommandName. Except for a few cases noted below any existing command by the same name is first deleted. If interp is in the process of being deleted Tcl_NRCreateCommand does not create any command, does not delete any command, and returns NULL.

Tcl_NREvalObj pushes a function that is like Tcl_EvalObjEx but consumes no space on the C stack.

Tcl_NREvalObjv pushes a function that is like Tcl_EvalObjv but consumes no space on the C stack.

Tcl_NRCmdSwap is like Tcl_NREvalObjv, but uses cmd, a token previously returned by Tcl_CreateObjCommand or Tcl_GetCommandFromObj, instead of resolving the first word of objv.

Tcl_NRExprObj pushes a function that evaluates objPtr as an expression in the same manner as Tcl_ExprObj but without consuming space on the C stack.

All of the functions return TCL_OK 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 TCL_ERROR and store a message as the interpreter's result.

Tcl_NRAddCallback pushes postProcPtr. The signature for Tcl_NRPostProc is:

typedef int
Tcl_NRPostProc(
        ClientData data[],
        Tcl_Interp *interp,
        int result);

data is a pointer to an array containing data0 through data3. result is the value returned by the previous function implementing part the routine.

EXAMPLE

int
TheCmdOldObjProc(
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,
    Tcl_Obj *const objv[])
{
    int result;
    Tcl_Obj *objPtr;

    ... preparation ...

    result = Tcl_EvalObjEx(interp, objPtr, 0);

    ... postprocessing ...

    return result;
}
Tcl_CreateObjCommand(interp, "theCommand",
        TheCmdOldObjProc, clientData, TheCmdDeleteProc);

To avoid consuming space on the C stack, TheCmdOldObjProc is renamed to TheCmdNRObjProc and the postprocessing step is split into a separate function, TheCmdPostProc, which is pushed onto the function stack. Tcl_EvalObjEx is replaced with Tcl_NREvalObj, which uses a trampoline instead of consuming space on the C stack. A new version of TheCmdOldObjProc is just a a wrapper that uses Tcl_NRCallObjProc to call TheCmdNRObjProc:

int
TheCmdOldObjProc(
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,
    Tcl_Obj *const objv[])
{
    return Tcl_NRCallObjProc(interp, TheCmdNRObjProc,
            clientData, objc, objv);
}

int
TheCmdNRObjProc
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,
    Tcl_Obj *const objv[])
{
    Tcl_Obj *objPtr;

    ... preparation ...

    Tcl_NRAddCallback(interp, TheCmdPostProc,
            data0, data1, data2, data3);
    /* data0 .. data3 are up to four one-word items to
     * pass to the postprocessing procedure */

    return Tcl_NREvalObj(interp, objPtr, 0);
}

int
TheCmdNRPostProc(
    ClientData data[],
    Tcl_Interp *interp,
    int result)
{
    /* data[0] .. data[3] are the four words of data
     * passed to Tcl_NRAddCallback */

    ... postprocessing ...

    return result;
}

Any function comprising a routine can push other functions, making it possible implement looping and sequencing constructs using the function stack.

SEE ALSO

KEYWORDS

COPYRIGHT