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NAME

Tk2portableTk - how to make your Tk source portable to other
interpreted languages.
 

Author

DESCRIPTION

The main problem with using the code developed for TCL with different languages is the absence of data types: almost anything is "char*". It makes automatic translation hopeless. However, if you "typedef" several new symbols to be "char*", you can still use your code in TCL, and it will make the automatic translation possible.

Another problem with the approach that ``everything is a string'' is impossibility to have a result that says ``NotApplicable'' without setting an error. Thus different Tk command return different string values that mean ``error happened'', like "", " " or "??". Other languages can be more flexible, so in portableTk you should inform the compiler that what you want to return means ``error'' (see ``Setting variables'').

Currently PortableTk uses several different approachs to simplify translation: several TCL functions that are especially dangerous to use are undefined, so you can easily find places that need to be updated to use Language-independent functions based on compiler warnings. Eventually a way to use these Language-independent functions under proper TCL will be also provided. The end of this document provides a starting point for such a project.  

Structure of pTk, porting your code

pTk is produced from Tk via a two-step process: first, some manual editing (the result is in the subdirectory "mTk"), and second, automatic conversion by the "munge" script (written in Perl). Thus the subdirectory "pTk/mTk" contains code with minimal possible difference from the virgin Tk code, so it is easier to merge(1) the differences between Tk versions into modified code.

It looks like the strategy for a portable code should be exactly opposite: starting from TCL-based code, apply "munge", and then hand-edit the resulting code. Probably it is also possible to target your code to portableTk from scratch, since this will make it possible to run it under a lot of Languages.

The only reason anyone would like to look into contents of "pTk/mTk" directory is to find out which constructs are not supported by "munge". On the other hand, "pTk" directory contains code that is conformant to portableTk, so you can look there to find example code.

"munge" is the script that converts most common Tk constructs to their "portableTk" equivalent. For your code to qualify, you should follow Tk conventions on indentation and names of variables, in particular, the array of arguments for the "...CmdProc" should be called "argv".

For details on what "munge" can do, see ``Translation of some TCL functions''.  

PortableTk API

Checking what you are running under

New types of configuration options

 TK_CONFIG_CALLBACK
 TK_CONFIG_LANGARG
 TK_CONFIG_SCALARVAR
 TK_CONFIG_HASHVAR
 TK_CONFIG_ARRAYVAR
 TK_CONFIG_IMAGE

You should use them instead of TK_CONFIG_STRING whenever appropriate. This allows your application to receive a direct representation of the corresponding resource instead of the string representation, if this is possible under given language.

???? It looks like "TK_CONFIG_IMAGE" and "TK_CONFIG_SCALARVAR" set variables of type "char*".  

Language data

Tcl_Obj *

is the main datatype of the language. This is a type that your C function gets pointers to for arguments when the corresponding Lang function is called. The corresponding config type is "TK_CONFIG_LANGARG".

This is also a type that keeps information about contents of Lang variable.

Var

Is a substitute for a "char *" that contains name of variable. In Lang it is an object that contains reference to another Lang variable.

LangResultSave

????

LangCallback

"LangCallback*" a substitute for a "char *" that contains command to call. The corresponding config type is "TK_CONFIG_CALLBACK".

LangFreeProc

It is the type that the "Lang_SplitList" sets. Before you call it, declare

    Args *args;
    LangFreeProc *freeProc = NULL;
    ...
    code = Lang_SplitList(interp, value,
        &argc, &args, &freeProc);

After you use the split values, call

    if (args != NULL && freeProc) (*freeProc)(argc,args);

It is not guaranteed that the "args" can survive deletion of "value".

Conversion

 LangCallback * LangMakeCallback(Tcl_Obj *)
 Tcl_Obj * LangCallbackArg(LangCallback *)
 char * LangString(Tcl_Obj *)

After you use the result of LangCallbackArg(), you should free it with "freeProc" "LANG_DYNAMIC" (it is not guaranteed that any change of "Tcl_Obj *" will not be reflected in <LangCallback>, so you cannot do LangSet...() in between, and you should reset it to "NULL" if you want to do any further assignments to this "Tcl_Obj *").

The following function returns the "Tcl_Obj *" that is a reference to "Var":

 Tcl_Obj * LangVarArg(Var)

???? It is very anti-intuitive, I hope the name is changed.

 int LangCmpCallback(LangCallback *a,Tcl_Obj * b)

(currently only a stub), and, at last,

 LangCallback * LangCopyCallback(LangCallback *)

Callbacks

 void LangFreeCallback(LangCallback *)
 int LangDoCallback(Tcl_Interp *,LangCallback *,
        int result,int argc, char *format,...)

The argument "format" of "LangDoCallback" should contain a string that is suitable for "sprintf" with optional arguments of "LangDoCallback". "result" should be false if result of callback is not needed.

 int LangMethodCall(Tcl_Interp *,Tcl_Obj *,char *method,
        int result,int argc,...)

????

Conceptually, "LangCallback*" is a substitute for ubiquitous "char *" in TCL. So you should use "LangFreeCallback" instead of "ckfree" or "free" if appropriate.  

Setting variables

 void LangFreeArg (Tcl_Obj *, Tcl_FreeProc *freeProc)
 Tcl_Obj *  LangCopyArg (Tcl_Obj *);
 void Tcl_AppendArg (Tcl_Interp *interp, Tcl_Obj *)
 void LangSetString(Tcl_Obj * *, char *s)
 void LangSetDefault(Tcl_Obj * *, char *s)

These two are equivalent unless s is an empty string. In this case "LangSetDefault" behaves like "LangSetString" with "s==NULL", i.e., it sets the current value of the Lang variable to be false.

 void LangSetInt(Tcl_Obj * *,int)
 void LangSetDouble(Tcl_Obj * *,double)

The Lang functions separate uninitialized and initialized data comparing data with "NULL". So the declaration for an "Tcl_Obj *" should look like

 Tcl_Obj * arg = NULL;

if you want to use this "arg" with the above functions. After you are done, you should use "LangFreeArg" with "TCL_DYNAMIC" as "freeProc".  

Language functions

int LangNull(Tcl_Obj *)

to check that an object is false;

int LangStringMatch(char *string, Tcl_Obj * match)

????

void LangExit(int)

to make a proper shutdown;

int LangEval(Tcl_Interp *interp, char *cmd, int global)

to call Lang "eval";

void Lang_SetErrorCode(Tcl_Interp *interp,char *code)

char *Lang_GetErrorCode(Tcl_Interp *interp)

char *Lang_GetErrorInfo(Tcl_Interp *interp)

void LangCloseHandler(Tcl_Interp *interp,Tcl_Obj * arg,FILE *f,Lang_FileCloseProc *proc)

currently stubs only;

int LangSaveVar(Tcl_Interp *,Tcl_Obj * arg,Var *varPtr,int type)

to save the structure "arg" into Lang variable *varPtr;

void LangFreeVar(Var var)

to free the result;

int LangEventCallback(Tcl_Interp *,LangCallback *,XEvent *,KeySym)

????

int LangEventHook(int flags)

void LangBadFile(int fd)

int LangCmpConfig(char *spec, char *arg, size_t length)

unsupported????;

void Tcl_AppendArg (Tcl_Interp *interp, Tcl_Obj *)

Another useful construction is

 Tcl_Obj * variable = LangFindVar(interp, Tk_Window tkwin, char *name);

After using the above function, you should call

 LangFreeVar(Var variable);

???? Note discrepancy in types!

If you want to find the value of a variable (of type "Tcl_Obj *") given the variable name, use "Tcl_GetVar(interp, varName, flags)". If you are interested in the string value of this variable, use "LangString(Tcl_GetVar(...))".

To get a C array of "Tcl_Obj *" of length "n", use

    Tcl_Obj * *args = LangAllocVec(n);
    ...
    LangFreeVec(n,args);

You can set the values of the "Tcl_Obj *"s using "LangSet..." functions, and get string value using "LangString".

If you want to merge an array of "Tcl_Obj *"s into one "Tcl_Obj *" (that will be an array variable), use

    result = Tcl_Merge(listLength, list);

Translation of some TCL functions

Tcl_AppendResult

does not take "(char*)NULL", but "NULL" as delimiter. Autoconverted.

Tcl_CreateCommand, Tcl_DeleteCommand

"Tk_CreateWidget", "Tk_DeleteWidget", the second argument is the window itself, not the pathname. Autoconverted.

sprintf(interp->result, %d %d %d %d,...)

"Tcl_IntResults(interp,4,0,...)". Autoconverted.

interp->result = 1;

"Tcl_SetResult(interp,"1", TCL_STATIC)". Autoconverted.

Reading interp->result

"Tcl_GetResult(interp)". Autoconverted.

interp->result = Tk_PathName(textPtr->tkwin);

"Tk_WidgetResult(interp,textPtr->tkwin)". Autoconverted.

Sequence Tcl_PrintDouble, Tcl_PrintDouble, ..., Tcl_AppendResult

Use a single command

 void Tcl_DoubleResults(Tcl_Interp *interp, int append,
        int argc,...);

"append" governs whether it is required to clear the result first.

A similar command for "int" arguments is "Tcl_IntResults".

Tcl_SplitList

Use "Lang_SplitList" (see the description above).

Translation back to TCL

 #include "ptcl.h"

before inclusion of "tk.h", and link the resulting code with "ptclGlue.c".

These files currently implement the following:

Additional config types:

 TK_CONFIG_CALLBACK
 TK_CONFIG_LANGARG
 TK_CONFIG_SCALARVAR
 TK_CONFIG_HASHVAR
 TK_CONFIG_ARRAYVAR
 TK_CONFIG_IMAGE

Types:

 Var, Tcl_Obj *, LangCallback, LangFreeProc.

Functions and macros:

 Lang_SplitList, LangString, LangSetString, LangSetDefault,
 LangSetInt, LangSetDouble Tcl_ArgResult, LangCallbackArg,
 LangSaveVar, LangFreeVar,
 LangFreeSplitProc, LangFreeArg, Tcl_DoubleResults, Tcl_IntResults,
 LangDoCallback, Tk_WidgetResult, Tcl_CreateCommand,
 Tcl_DeleteCommand, Tcl_GetResult.

Current implementation contains enough to make it possible to compile "mTk/tkText*.[ch]" with the virgin Tk.  

New types of events ????

 TK_EVENTTYPE_NONE
 TK_EVENTTYPE_STRING
 TK_EVENTTYPE_NUMBER
 TK_EVENTTYPE_WINDOW
 TK_EVENTTYPE_ATOM
 TK_EVENTTYPE_DISPLAY
 TK_EVENTTYPE_DATA

and a function

 char * Tk_EventInfo(int letter,
            Tk_Window tkwin, XEvent *eventPtr,
            KeySym keySym, int *numPtr, int *isNum, int *type,
            int num_size, char *numStorage)

Checking for trouble

Additional API

ListFactory

The type for construction of dynamic lists is "ListFactory". The API below is a counterpart of the API for construction of dynamic lists in TCL:

 void ListFactoryInit(ListFactory *)
 void ListFactoryFinish(ListFactory *)
 void ListFactoryFree(ListFactory *)
 Tcl_Obj * * ListFactoryArg(ListFactory *)
 void ListFactoryAppend(ListFactory *, Tcl_Obj * *arg)
 void ListFactoryAppendCopy(ListFactory *, Tcl_Obj * *arg)
 ListFactory * ListFactoryNewLevel(ListFactory *)
 ListFactory * ListFactoryEndLevel(ListFactory *)
 void ListFactoryResult(Tcl_Interp *, ListFactory *)

The difference is that a call to "ListFactoryFinish" should precede the actual usage of the value of "ListFactory", and there are two different ways to append an "Tcl_Obj *" to a "ListFactory": ListFactoryAppendCopy() guarantees that the value of "arg" is copied to the list, but ListFactoryAppend() may append to the list a reference to the current value of "arg". If you are not going to change the value of "arg" after appending, the call to ListFactoryAppend may be quicker.

As in TCL, the call to ListFactoryFree() does not free the "ListFactory", only the objects it references.

The functions ListFactoryNewLevel() and ListFactoryEndLevel() return a pointer to a "ListFactory" to fill. The argument of ListFactoryEndLevel() cannot be used after a call to this function.  

DStrings

Accessing Tcl_Obj *s

 double LangDouble(Tcl_Obj *)
 int LangInt(Tcl_Obj *)
 long LangLong(Tcl_Obj *)
 int LangIsList(Tcl_Obj * arg)

The function LangIsList() is supported only partially under TCL, since there is no data types. It checks whether there is a space inside the string "arg".  

Assigning numbers to Tcl_Obj *s

   dArgBuffer;

and assign this buffer to the "Tcl_Obj *" by

   void LangSetDefaultBuffer(Tcl_Obj * *)

You can also create the buffer(s) manually and assign them using

   void LangSetBuffer(Tcl_Obj * *, char *)

This is the only choice if you need to assign numeric values to several "Tcl_Obj *"s simultaneously. The advantage of the first approach is that the above declarations can be made "nop"s in different languages.

Note that if you apply "LangSetDefaultBuffer" to an "Tcl_Obj *" that contains some value, you can create a leak if you do not free that "Tcl_Obj *" first. This is a non-problem in real languages, but can be a trouble in "TCL", unless you use only the above API.  

Creating new Tcl_Obj *s

 void LangNewArg(Tcl_Obj * *, LangFreeProc *)

The API for creating a new "Tcl_Obj *" is absent. Just initialize "Tcl_Obj *" to be "NULL", and apply one of "LangSet..." methods.

After you use this "Tcl_Obj *", it should be freed thusly:

"LangFreeArg(arg, freeProc)".  

Evaluating a list

 int LangArgEval(Tcl_Interp *, Tcl_Obj * arg)

Here "arg" should be a list to evaluate, in particular, the first element should be a "LangCallback" massaged to be an "Tcl_Obj *". The arguments can be send to the subroutine by reference or by value in different languages.  

Getting result as Tcl_Obj *

Index

NAME

Author

DESCRIPTION

Structure of pTk, porting your code

PortableTk API

Checking what you are running under

New types of configuration options

Language data

Conversion

Callbacks

Setting variables

Language functions

Translation of some TCL functions

Translation back to TCL

New types of events ????

Checking for trouble

Additional API

ListFactory

DStrings

Accessing Tcl_Obj *s

Assigning numbers to Tcl_Obj *s

Creating new Tcl_Obj *s

Evaluating a list

Getting result as Tcl_Obj *

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