Tk2portableTk - how to make your Tk source portable to other interpreted languages.
Ilya Zakharevich <ilya@math.ohio-state.edu> 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
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.
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 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 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_IMAGE and TK_CONFIG_SCALARVAR set
variables of type char*.
The following data types are defined:
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
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.
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
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 *)
Above we have seen the new datatype LangCallback and the
corresponding Config option TK_CONFIG_CALLBACK. The following
functions are provided for manipulation of LangCallbacks:
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.
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.
Use
int LangNull(Tcl_Obj *)
int LangStringMatch(char *string, Tcl_Obj * match)
void LangExit(int)
int LangEval(Tcl_Interp *interp, char *cmd, int global)
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)
int LangSaveVar(Tcl_Interp *,Tcl_Obj * arg,Var *varPtr,int type)
arg into Lang variable *varPtr;
void LangFreeVar(Var var)
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
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);
We mark items that can be dealt with by munge by Autoconverted.
Tcl_AppendResult
(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.
interp->result
Tcl_GetResult(interp). Autoconverted.
interp->result = Tk_PathName(textPtr->tkwin);
Tk_WidgetResult(interp,textPtr->tkwin). Autoconverted.
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
Lang_SplitList (see the description above).
To use your portableTk program with TCL, put
#include "ptcl.h"
before inclusion of tk.h, and link the resulting code with
ptclGlue.c.
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 sprintf and 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).
ListFactory
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.
Tcl_Obj *s
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 arg.
Tcl_Obj *s
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
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 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.
Tcl_Obj *s
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 LangSet... methods.
After you use this Tcl_Obj *, it should be freed thusly:
LangFreeArg(arg, freeProc).
Use
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.
Tcl_Obj *
Use 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 freeProc LANG_DYNAMIC (you can do LangSet...() in between).