MzCOM.exe is a Windows COM (i.e., Component Object Model) class wrapper for PLT Scheme.
During normal installation of MzCOM, the executable is registered as a COM object automatically. If you move the PLT Scheme installation folder, re-register MzCOM.exe with
The MzCOM.exe executable find DLLs and PLT Scheme library collections relative to its own path.
To load a COM object, COM hosts require a COM class name or a ProgID. MzCOM has the class name "MzObj Class" and the ProgID "MzCOM.MzObj.‹version›", where ‹version› is 4.2.4.
In the Visual BASIC 6 environment, from the Project|References (VB6), check MzCOM 1.0 Type Library. In Visual BASIC .NET, choose Project|Add Reference, and from the COM tab, select MzCOM 1.0 Type Library. In your code, declare a variable, then assign to it:
DIM schemeObject AS MzObj
SET schemeObject = NEW MzObj
From Visual C++:
CoCreateInstance(clsid,NULL,CLSCTX_SERVER,IID_IMzObj, (void **)&pIMzObj);
where <version> is the version number. You’ll need the definition of IID_IMzObj (see GUIDs). The header file "mzcom.h" is generated as "src\worksp\mzcom\" when building from the PLT Scheme source distribution. The above C/C++ code is for illustration; your actual code should check return values, of course.
Using mysterx to manipulate COM objects within Scheme, you can load MzCOM with either
(cci/coclass "MzObj Class")
Consult your documentation for loading MzCOM into other COM environments. MzCOM is compiled as a “dual-mode” class, meaning its methods may be called directly or by using OLE Automation.
When compiled from the PLT Scheme source distibrution, the directory "src\worksp\mzcom\" contains the file "MzCOM_i.c" that contains GUIDs for MzCOM. Those GUIDs are as follows:
const IID IID_IMzObj =
const IID LIBID_MZCOMLib =
const IID DIID__IMzObjEvents =
const CLSID CLSID_MzObj =
which represent the IMzObj interface, the MzCOM type library, the IMzObjEvents interface, and the MzObj class, respectively.
MzCOM support three COM methods:
Takes no arguments and displays an informational dialog.
Takes and returns BSTRs (BASIC strings). The returned value is the result of evaluating the input expression, formatted as a string. The input string may contain several S-expressions. The embedded PLT Scheme updates its environment with each evaluation. Therefore, it is possible to define procedures in a call to Eval, and use the procedures in subsequent calls.
Resets the Scheme environment to the initial environment. Also, the custodian for the primary Scheme thread is invoked, shutting all its managed values.
MzCOM supports a single event.
When an error occurs in MzCOM, it creates a COM error object. C and C++ clients can use GetErrorInfo to retrieve error information. Clients implemented in other languages typically have some equivalent means to obtain COM error information.
The PLT Scheme evaluator runs in a Win32 thread created when MzCOM is loaded. If an expression kills the primary MzScheme thread, as in
then the evaluator Win32 thread is also killed. When that happens, subsequent calls to Eval() will fail.
MzCOM was developed in response to a query by Andre Van Meulebrouck. Andre also did extensive testing with Visual BASIC.