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Using Tk extensions under caml/labltk
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Date: 2000-03-23 (12:39)
From: Michael Hohn <hohn@m...>
Subject: Using Tk extensions under caml/labltk

Recently, I needed to use the BLT extension to Tk.  Since all my data comes
from ocaml, and there is a fair amount of data, I wrote a simple C interface.
Below are the steps I took under ocaml-2.04.
My questions are:

1.  Why is tcl_eval not exported by default (in protocol.mli)?  I
    don't like Tcl much, but 
    for trivial commands like "package require blt", I don't see a
    problem with direct string evaluation.
    Also, it would be nice to have some interactive control over caml programs
    compiled to native code; wouldn't Tcl work well for this?

2.  Apparently, most high-level widget interfaces are defined in
    otherlibs/labltk/Widgets.src, with special routines in 
    otherlibs/labltk/builtin/* and general low level support in 
    Since I only needed a small subset of the BLT commands and
    couldn't quite figure out the details in this setup, I used direct
    string evaluation with some embedded caml callbacks, e.g.

    tcl (g.g_name ^ " element create line_" ^ xv ^ " \
	     -xdata "^ xv ^ " -ydata "^ yv ^ " \
	     -symbol {} \
	     -pixels 0.1c \
	     -color "^
	     (domain_color dom) ^ "\n")

    Needless to say, a clean wrapper would be better.	   

    Is there a particular approach to be followed when adding new

    Or better yet, does someone have a *documented* example for the
    addition of a widget requiring additions in all three places :) ?


Here are my notes:
    To really use Tcl with camltk requires some special
    installation steps. 
    1.  Produce the include file camltk41/camltk.h
	This include file must be manually installed from the
	ocamltk41 distribution; e.g.
	    cp ocamltk41/support/camltk.h /usr/local/lib/ocaml/camltk41
    2.  The caml header file protocol.mli is ....  It does not
	provide the (very useful) function tcl_eval.
	To fix this, do:
	    cd ./otherlibs/labltk/support
	    [ cd ocamltk41/support in 2.04 ]
	    cat >>  protocol.mli <<EOF
    val tcl_eval : string -> string
	BEFORE compiling the ocamltk41.
	[Doing this after and re-installing only changed files causes
	    inexplicable core dumps later.]
	     tcl_eval "package require BLT"
	     tkEval [| TkToken "package"; TkToken "require"; TkToken "BLT"
	 On longer inputs, this would not be amusing... ]
Using these, the following worked:
       set_blt_vector name array --
	   set/create the BLT array "name" and
	   set its entries to the values in <array>.
    external set_blt_vector : string -> float array -> unit = "set_blt_vector_" 
And the C file:
    #include <tcl.h>
    #include <blt.h>
    #include "caml/mlvalues.h"
       This include file must have been manually installed from the
       ocamltk41 distribution; e.g.
       cp ocamltk41/support/camltk.h /usr/local/lib/ocaml/camltk41
       Some code taken from the ocaml/fortran interface example.
    #include "camltk41/camltk.h"
    value set_blt_vector_(value vName, value vA)
	char *name  = String_val(vName);
	 * Do we have a native, ocamlopt array or a bytecode, ocamlc one?
	int isNative = Tag_val(vA) == Double_array_tag;
	 * How big is it?
	int arrayLength =
	isNative ? Bosize_val(vA) / sizeof(double) : Wosize_val(vA);
	Blt_Vector *vecPtr;
	double *newArr;
	 * Make sure the Tcl interpreter exists.
	if (cltclinterp == NULL) 
	failwith("Tcl not initialized.");
	 * Make [newArr] point to a C-friendly version of [vA]
	/* Allocate the array on the C heap, and let BLT free() it (see
	   below). */
	newArr = (double *)malloc(arrayLength * sizeof(double));
	if (isNative)
	    /* ocamlopt-style array: copy it using [Double_field] */
		int i;
		    for (i = 0; i < arrayLength; ++i)
			newArr[i] = Double_field(vA, i);
	    /* ocamlc-style array: copy it using [Double_val(Field(...))]
	    int i;
		for (i = 0; i < arrayLength; ++i)
		    newArr[i] = Double_val(Field(vA, i));
	 * Prepare the BLT vector. 
	if (Blt_VectorExists(cltclinterp, name))  {
	if (Blt_GetVector(cltclinterp, name, &vecPtr) != TCL_OK) 
	    failwith("Tcl error.");
	} else {
	if (Blt_CreateVector(cltclinterp, name, 0, &vecPtr) != TCL_OK) 
	    failwith("Tcl error.");
	 * Reset the vector to use the new array. Clients will be notified
	 * when Tk is idle. 
	 * TCL_DYNAMIC tells the vector to free the memory allocated
	 * if it needs to reallocate or destroy the vector.
	if (Blt_ResetVector(vecPtr, newArr, arrayLength, arrayLength,
				    TCL_DYNAMIC) != TCL_OK)
				    failwith("Tcl error.");
	return Val_unit;