Tk2portableTk - how to make your Tk source portable to other interpreted languages.
Ilya Zakharevich <firstname.lastname@example.org> has contributed most of this document. Many thanks.
PortableTk is an attempt to make Tk useful from other languages. Currently tk4.0 runs under Perl using this approach. Below, Lang is the notation for an external language to which PortableTk glues Tk code.
The main problem with using the code developed for TCL with different languages is the absence of data types: almost anything is
It makes automatic translation hopeless.
typedef several new symbols to be
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",
" " 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.
pTk, that is a port of Tk, is very special with respect to porting of other code to portableTk. The problem is that currently there is very little hope to merge the modifications back into Tk, so a special strategy is needed to maintain this port. Do not use this strategy to port your own code.
pTk is produced from Tk via a two-step process: first,
some manual editing (the result is in the subdirectory
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,
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
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
For your code to qualify,
you should follow Tk conventions on indentation and names of variables,
the array of arguments for the
...CmdProc should be called
For details on what
munge can do,
see "Translation of some TCL functions".
PortableTk provides a symbol
If this symbol is defined,
your source is compiled with it.
PortableTk defines several 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_SCALARVAR set variables of type
The following data types are defined:
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
This is also a type that keeps information about contents of Lang variable.
Is a substitute for a
char * that contains name of variable. In Lang it is an object that contains reference to another Lang variable.
LangCallback* a substitute for a
char * that contains command to call. The corresponding config type is
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
The following macros and functions are used for conversion between strings and the additional types:
LangCallback * LangMakeCallback(Tcl_Obj *) Tcl_Obj * LangCallbackArg(LangCallback *) char * LangString(Tcl_Obj *)
After you use the result of LangCallbackArg(), you should free it with
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
The following function returns the
Tcl_Obj * that is a reference to
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 *)
Above we have seen the new datatype
LangCallback and the corresponding Config option
TK_CONFIG_CALLBACK. The following functions are provided for manipulation of
void LangFreeCallback(LangCallback *) int LangDoCallback(Tcl_Interp *,LangCallback *, int result,int argc, char *format,...)
LangDoCallback should contain a string that is suitable for
sprintf with optional arguments of
result should be false if result of callback is not needed.
int LangMethodCall(Tcl_Interp *,Tcl_Obj *,char *method, int result,int argc,...)
LangCallback* is a substitute for ubiquitous
char * in TCL. So you should use
LangFreeCallback instead of
free if appropriate.
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
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
int LangNull(Tcl_Obj *)
to check that an object is false;
int LangStringMatch(char *string, Tcl_Obj * match)
to make a proper shutdown;
int LangEval(Tcl_Interp *interp, char *cmd, int global)
to call Lang
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
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)
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
???? 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
To get a C array of
Tcl_Obj * of length
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
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);
We mark items that can be dealt with by
munge by Autoconverted.
does not take
NULL as delimiter. Autoconverted.
Tk_DeleteWidget, the second argument is the window itself, not the pathname. Autoconverted.
sprintf(interp->result, "%d %d %d %d",...)
interp->result = "1";
Tcl_SetResult(interp,"1", TCL_STATIC). Autoconverted.
interp->result = Tk_PathName(textPtr->tkwin);
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
Lang_SplitList (see the description above).
To use your portableTk program with TCL, put
before inclusion of
tk.h, and link the resulting code with
These files currently implement the following:
TK_CONFIG_CALLBACK TK_CONFIG_LANGARG TK_CONFIG_SCALARVAR TK_CONFIG_HASHVAR TK_CONFIG_ARRAYVAR TK_CONFIG_IMAGE
Var, Tcl_Obj *, LangCallback, LangFreeProc.
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.
PortableTk defines following 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)
If you start with working TCL code, you can start convertion using the above hints. Good indication that you are doing is OK is absence of
sscanf in your code (at least in the part that is working with interpreter).
What is described here is not included into base portableTk distribution. Currently it is coded in TCL and as Perl macros (core is coded as functions, so theoretically you can use the same object files with different interpreted languages).
Dynamic arrays in TCL are used for two different purposes: to construct strings, and to construct lists. These two usages will have separate interfaces in other languages (since list is a different type from a string), so you should use a different interface in your code.
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.
Production of strings are still supported in portableTk.
The following functions for getting a value of an
Tcl_Obj * may be provided:
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
While LangSetDouble() and LangSetInt() are supported ways to assign numbers to assign an integer value to a variable, for the sake of efficiency under TCL it is supposed that the destination of these commands was massaged before the call so it contains a long enough string to sprintf() the numbers inside it. If you are going to immediately use the resulting
Tcl_Obj *, the best way to do this is to declare a buffer in the beginning of a block by
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
nops 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.
The API for creating a new
Tcl_Obj * is
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
After you use this
Tcl_Obj *, it should be freed thusly:
int LangArgEval(Tcl_Interp *, Tcl_Obj * arg)
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.
Tcl_ArgResult. It is not guaranteed that result survives this operation, so the
Tcl_Obj * you get should be the only mean to access the data from this moment on. After you use this
Tcl_Obj *, you should free it with
LANG_DYNAMIC (you can do LangSet...() in between).