Interfacing REXX with Other Programming Languages: Techniques and Best Practices

Hello, fellow programming enthusiasts! In this blog post, I will introduce you to the Interfacing REXX with Other Languages – with other programming languages.

REXX can seamlessly communicate with languages like C, Java, and Python, enabling cross-language integration for enhanced functionality. Understanding how to pass data, execute external routines, and manage interoperability is crucial for building efficient and flexible applications. I will walk you through key interfacing methods, including dynamic linking, API calls, and script execution. By the end, you’ll have a solid understanding of how to extend REXX’s capabilities through cross-language integration. Let’s get started!

An Introduction to Interfacing REXX with Other Languages

REXX is a flexible scripting language that can interface with other programming languages for enhanced functionality. This can be achieved using external commands, dynamic link libraries (DLLs), and APIs. Through the ADDRESS statement, REXX can call programs written in C, Java, or Python, enabling seamless integration. It also supports inter-process communication, making it suitable for automation and data exchange. By leveraging these features, developers can extend REXX capabilities, integrate it into complex systems, and optimize workflows across different platforms.

What is Interfacing REXX with Other Languages?

REXX (Restructured Extended Executor) is a powerful scripting language primarily used for automation, data processing, and system administration. However, REXX’s true potential is unlocked when it interacts with other programming languages. By interfacing REXX with languages like C, C++, Java, Python, or even assembly, developers can extend REXX’s capabilities, integrate it with existing software systems, and leverage the strengths of multiple languages in a unified workflow.

Methods of Interfacing REXX with Other Languages

REXX supports multiple mechanisms to interact with other programming languages. These methods include:

1. Calling External Programs (Shell Execution)
2. Using REXX External Functions (REXX Function Packages)
3. Interfacing via Dynamic Link Libraries (DLLs) or Shared Objects (SOs)
4. Using Inter-Process Communication (IPC)
5. Embedding REXX in Other Languages
6. Using Object-Oriented Bridges (Java, COM, .NET, etc.)
7. Using APIs like REXX SAA API (System Application Architecture)

Let’s explore each in detail.

Calling External Programs (Shell Execution)

The simplest way to interface REXX with another language is by calling external programs or scripts written in other languages via system commands.

Example: Calling Python from REXX

/* Call an external Python script */
'python myscript.py'

• This executes myscript.py as a separate process.
• The output of the script can be captured using command redirection.

Example: Calling C Program

'myprogram.exe'

• A compiled C program (myprogram.exe on Windows or ./myprogram on Linux) can be executed from REXX.

This method is simple but has limitations, as it does not provide direct function calls or variable sharing.

Using REXX External Functions (REXX Function Packages)

REXX allows developers to create external functions that extend its functionality. These functions can be written in C, C++, or other languages and loaded dynamically when needed.

Example: Writing an External Function in C

1. Write a C function (e.g., addnums.c)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "rexxsaa.h"

RexxFunctionHandler addnums;

unsigned long addnums(
    const char *name,
    unsigned long numargs,
    RXSTRING args[],
    const char *queuename,
    RXSTRING *retstr)
{
    if (numargs != 2) return INVALID_ROUTINE;

    int a = atoi(args[0].strptr);
    int b = atoi(args[1].strptr);
    int sum = a + b;

    sprintf(retstr->strptr, "%d", sum);
    retstr->strlength = strlen(retstr->strptr);
    
    return 0;
}

2. Compile it into a shared library (addnums.dll on Windows or addnums.so on Linux).
3. Load and use the function in REXX:

call RxFuncAdd 'addnums', 'addnums', 'addnums'
result = addnums(10, 20)
say "Sum: " result

• RxFuncAdd registers the function.
• addnums(10, 20) calls the C function.

This method provides direct communication between REXX and C.

Interfacing via Dynamic Link Libraries (DLLs) or Shared Objects (SOs)

REXX can interface with Dynamic Link Libraries (DLLs) on Windows or Shared Objects (SOs) on Linux to call external functions.

Example: Calling a C++ Function from REXX using a DLL

1. Write a C++ function (multiply.cpp)

#include <iostream>

extern "C" __declspec(dllexport) int multiply(int a, int b) {
    return a * b;
}

2. Compile it into a DLL (multiply.dll).
3. Load and call the function in REXX

call RxFuncAdd 'multiply', 'multiply.dll', 'multiply'
result = multiply(5, 4)
say "Multiplication Result: " result

This method provides a robust way to extend REXX with external libraries.

Using Inter-Process Communication (IPC)

REXX can communicate with other programs via pipes, sockets, message queues, or shared memory.

Example: Communicating via Pipes (Calling a Python Script and Capturing Output)

pyout = linein('python myscript.py')
say "Python Output: " pyout

• linein reads the output from myscript.py.

Example: Using TCP/IP Sockets

REXX can send and receive data over networks using TCP/IP sockets to communicate with a server written in another language like Python or C.

Embedding REXX in Other Languages

Some applications require embedding REXX within another programming language, allowing the external language to invoke REXX scripts.

Example: Calling REXX from C

#include "rexxsaa.h"

void call_rexx_script() {
    CONSTRXSTRING rexx_script;
    RXSTRING retstr;
    
    rexx_script.strptr = "say 'Hello from REXX'";
    rexx_script.strlength = strlen(rexx_script.strptr);

    RexxStart(0, NULL, "myscript.rex", &rexx_script, NULL, RXCOMMAND, NULL, NULL, &retstr);
}

• RexxStart() executes a REXX script from C.

This allows seamless integration of REXX into a C/C++ program.

Using Object-Oriented Bridges (Java, COM, .NET, etc.)

REXX can interact with Java, .NET, and COM objects to access object-oriented capabilities.

Example: Calling a Java Method from REXX using BSF4REXX

BSF4REXX (Bean Scripting Framework for REXX) enables calling Java methods from REXX.

1. Install BSF4REXX
2. Write a REXX script calling Java

call bsfCreateObject "java.lang.String", "Hello from Java"
say result.toUpperCase()

• This allows REXX to use Java objects and methods.

Example: Calling .NET Methods

REXX can interact with COM/.NET objects using OLEObject.

obj = CreateObject("Excel.Application")
obj.Visible = 1

• This launches Microsoft Excel from REXX.

Why do we need to Interface REXX with Other Programming Languages?

Interfacing REXX with other programming languages enhances its capabilities by allowing it to perform tasks that would otherwise be inefficient or impossible. Below are the key reasons why integrating REXX with other languages is essential:

1. Extending Functionality

REXX is a powerful scripting language but lacks direct access to low-level system functionalities like hardware control and memory management. By interfacing with languages like C or C++, REXX can leverage their capabilities to perform complex operations such as device driver interaction and system-level programming.

2. Performance Optimization

While REXX is excellent for scripting and automation, it is not optimized for high-performance computing. Computationally intensive tasks, such as mathematical calculations or data processing, can be offloaded to faster languages like C, C++, or Java, significantly improving execution speed and efficiency.

3. Accessing External Libraries and APIs

Modern software development relies on a vast ecosystem of libraries and APIs written in languages like Python, Java, or C. By interfacing REXX with these languages, developers can integrate functionalities such as machine learning, data visualization, and web services that are not natively available in REXX.

4. Integrating with Legacy Systems

Many enterprises use legacy systems that rely on REXX for scripting and automation. However, core business logic is often implemented in other languages. Interfacing allows REXX to communicate with these legacy and modern systems seamlessly, ensuring smooth migration and system interoperability.

5. Enabling Cross-Platform Compatibility

REXX is widely used in IBM mainframes and OS/2 environments but has limited direct support for modern operating systems. By integrating with other languages like Python, Java, or C#, developers can build cross-platform applications that work on Windows, Linux, macOS, and cloud-based infrastructures.

6. Enhancing Automation and Scripting Capabilities

REXX is widely used for system automation, but it has limitations in handling GUI automation and web interactions. By integrating with languages like Python (Selenium for web automation) or AutoIt (for GUI automation), REXX scripts can automate complex workflows involving web pages, databases, and graphical applications.

7. Utilizing Object-Oriented Programming (OOP) Features

REXX is primarily a procedural language and lacks built-in object-oriented programming (OOP) support. By interfacing with languages such as Java, C++, or Python, developers can incorporate OOP concepts like encapsulation, inheritance, and polymorphism, enabling the development of scalable and modular applications.

8. Facilitating Inter-Process Communication (IPC)

Modern applications often require multiple processes to communicate and share data. By using IPC mechanisms such as sockets, message queues, and shared memory, REXX can interact with other processes running different programming languages, enabling real-time data exchange and distributed computing.

9. Supporting Web and Cloud Integration

REXX does not have built-in support for web development or cloud computing. By interfacing with languages like Python (Flask, Django), JavaScript (Node.js), or PHP, REXX can send HTTP requests, process web data, and interact with cloud-based APIs, making it useful for modern web and cloud applications.

10. Improving Data Handling and Analysis

Although REXX is effective for text and file processing, it lacks advanced data analysis and visualization features. By integrating with Python (Pandas, NumPy), R (statistical analysis), or SQL databases, REXX can efficiently handle large datasets, perform analytics, and generate reports with graphical representations.

Example of Interfacing REXX Programming with Other Languages

Interfacing REXX with other programming languages enhances its capabilities, allowing it to integrate with system-level operations, high-performance computing, modern APIs, and legacy systems. This guide provides in-depth explanations and step-by-step examples of how REXX can interact with other programming languages.

1. Calling a Python Script from REXX

Python is widely used for automation, data processing, and AI. REXX can call a Python script to execute complex operations.

Example Scenario:

Suppose you want to use Python to process some data and return the result to REXX.

Python Script (myscript.py)

import sys

# Python script that prints a message
print("Hello from Python!")

REXX Script (call_python.rex)

/* Calling a Python script from REXX */
command = "python myscript.py"
output = linein(command)
say "Output from Python: " output

1. Executing External Commands: The REXX script runs a system command (python myscript.py).
2. Capturing Output: The output from Python is read using linein().
3. Displaying Results: The output is printed in the REXX console.

This approach enables REXX to integrate with Python’s vast ecosystem, including machine learning and web APIs.

2. Calling a C Function from REXX Using a Shared Library

C is known for its efficiency and system-level operations. REXX can call a C function for tasks that require speed and direct memory access.

Example Scenario:

You want to create a simple C function that adds two numbers and call it from REXX.

C Code (addnums.c)

#include <stdio.h>
#include <stdlib.h>
#include "rexxsaa.h"

RexxFunctionHandler addnums;

unsigned long addnums(
    const char *name,
    unsigned long numargs,
    RXSTRING args[],
    const char *queuename,
    RXSTRING *retstr)
{
    if (numargs != 2) return INVALID_ROUTINE;

    int a = atoi(args[0].strptr);
    int b = atoi(args[1].strptr);
    int sum = a + b;

    sprintf(retstr->strptr, "%d", sum);
    retstr->strlength = strlen(retstr->strptr);
    
    return 0;
}

Steps to Compile (Linux & Windows)

Linux:

gcc -shared -o addnums.so -fPIC addnums.c

Windows:

gcc -shared -o addnums.dll addnums.c

REXX Script (call_c.rex)

/* Register the C function */
call RxFuncAdd 'addnums', 'addnums.so', 'addnums'

/* Call the function */
result = addnums(10, 20)
say "Sum from C function: " result

1. Compiling the C Code: The C function is compiled into a shared library (.so for Linux, .dll for Windows).
2. Registering the Function: RxFuncAdd makes the C function available in REXX.
3. Calling the Function: The REXX script passes arguments and gets the sum.

This allows REXX to use high-performance C functions for computation-heavy tasks.

3. Calling a Java Method from REXX Using BSF4REXX

Java is widely used in enterprise applications. REXX can interact with Java using the BSF4REXX library.

Example Scenario:

You want to call a Java method from REXX.

Java Code (HelloJava.java)

public class HelloJava {
    public static String greet() {
        return "Hello from Java!";
    }
}

Compile the Java Class:

javac HelloJava.java

REXX Script (call_java.rex)

/* Load the Java class */
call bsfCreateObject "HelloJava"

/* Call the Java method */
message = bsfCallStaticMethod("HelloJava", "greet")

/* Display the output */
say "Java says: " message

1. Loading the Java Class: bsfCreateObject loads the Java class into REXX.
2. Calling Java Methods: bsfCallStaticMethod executes Java methods from REXX.
3. Returning Data: The Java function returns a string, which REXX captures.

This allows REXX to leverage Java’s powerful object-oriented features.

4. Accessing a Web API Using REXX and cURL

REXX can interact with web services by using cURL.

Example Scenario:

Fetch data from an API using REXX.

REXX Script (call_api.rex)

/* Fetch API data using cURL */
url = "https://api.github.com"
command = 'curl -s "' || url || '"'
output = linein(command)

/* Display API response */
say "API Response: " output

1. Calling a Web API: cURL is used to send an HTTP request.
2. Reading the Response: linein() captures API output.
3. Displaying Data: The API response is printed in REXX.

This method allows REXX to work with web services like REST APIs.

5. Using Inter-Process Communication (IPC) with Sockets

IPC enables REXX to communicate with other applications using sockets.

Example Scenario:

A Python server receives a message from REXX and responds.

Python Server (server.py)

import socket

server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.bind(("localhost", 12345))
server.listen(1)

conn, addr = server.accept()
data = conn.recv(1024).decode()
conn.sendall(f"Hello from Python! You said: {data}".encode())
conn.close()

REXX Client (socket_client.rex)

/* Open socket connection */
say 'Connecting to server...'
server = 'echo "Hello Python!" | nc localhost 12345'
response = linein(server)
say "Server response: " response

1. Python Server: Listens on localhost:12345 and responds.
2. REXX Client: Sends a message using Netcat (nc) and receives a response.

This technique is useful for real-time communication between REXX and other applications.

Advantages of Interfacing REXX Programming with Other Languages

Here are the advantages of interfacing REXX programming with other languages:

1. Expanded Functionality: REXX has a simple syntax but lacks advanced features found in other languages. By interfacing with languages like C, Python, or Java, developers can leverage powerful libraries, frameworks, and APIs to extend REXX’s capabilities.
2. Enhanced Performance: While REXX is an interpreted language, interfacing with compiled languages (e.g., C or C++) allows execution of high-performance tasks, improving efficiency for compute-intensive operations.
3. Access to System-Level Operations: REXX can interact with low-level system functions through languages like C, enabling access to memory management, device drivers, and system calls that REXX alone cannot perform.
4. Improved GUI Development: Since REXX lacks built-in GUI support, integrating with Java, Python (Tkinter, PyQt), or C# (WinForms) enables the creation of modern graphical user interfaces (GUIs) for better user interaction.
5. Better Database Connectivity: By interfacing with SQL-based languages or database drivers from Python, Java, or C, REXX scripts can efficiently access and manage databases, improving data storage and retrieval.
6. Cross-Platform Compatibility: REXX can be integrated with platform-independent languages like Java, making it more adaptable across Windows, Linux, and mainframes without major modifications.
7. Easier Web Integration: Web technologies like PHP, JavaScript, or Python can extend REXX’s ability to interact with web servers, REST APIs, and web applications, enabling automation and data exchange over the internet.
8. Seamless Automation and Scripting: REXX scripts can automate tasks while delegating specialized functions (e.g., machine learning with Python, advanced math with MATLAB) to external programs, enhancing automation capabilities.
9. Code Reusability and Maintainability: Instead of rewriting existing logic in REXX, interfacing allows developers to reuse well-tested modules from other languages, reducing development effort and maintenance costs.
10. Broader Industry Adoption: Interfacing with other languages makes REXX more relevant in modern computing, ensuring it remains useful in industries such as mainframe computing, data processing, and system automation.

Disadvantages of Interfacing REXX Programming with Other Languages

Here are the disadvantages of interfacing REXX programming with other languages:

1. Increased Complexity: Interfacing REXX with other languages requires additional coding, configuration, and debugging, making the overall development process more complex compared to writing a standalone REXX script.
2. Performance Overhead: Calling external programs or libraries introduces communication overhead, such as process creation, data conversion, and inter-process communication (IPC), which can slow down execution.
3. Dependency Management Issues: Interfacing requires external libraries, compilers, or runtime environments, making it harder to ensure all dependencies are available and properly configured across different systems.
4. Portability Challenges: Some integrations may work well on one operating system (e.g., Windows) but require modifications or may not function at all on others (e.g., Linux or z/OS), reducing cross-platform compatibility.
5. Error Handling Complexity: Debugging errors in a multi-language environment is more difficult, as errors may originate from the REXX script, the external program, or the communication layer between them.
6. Security Risks: Improper handling of external calls (e.g., shell commands, database queries) may introduce security vulnerabilities, such as code injection, unauthorized access, or system instability.
7. Data Format Incompatibility: Different programming languages use different data types and structures, requiring additional conversion logic, which can lead to data loss, incorrect processing, or increased development time.
8. Dependency on External Tools: If the external language or library gets deprecated, upgraded, or replaced, REXX scripts relying on them may stop working, requiring frequent maintenance and updates.
9. Limited Support for Advanced Interfacing: REXX does not natively support complex integration methods (e.g., multithreading, direct memory access), limiting its ability to interact efficiently with modern programming frameworks.
10. Increased Learning Curve: Developers must learn multiple languages, integration techniques, and troubleshooting methods, which increases the time and effort needed to develop and maintain hybrid applications.

Future Development and Enhancement of Interfacing REXX Programming with Other Languages

Here are the future developments and enhancements that could improve interfacing REXX with other languages:

1. Standardized API and Library Support: Introducing a well-documented API framework for integrating REXX with modern languages like Python, Java, and C++ would make cross-language communication easier and more reliable.
2. Improved Cross-Platform Compatibility: Enhancements in REXX interpreters could provide built-in support for seamless interaction across different operating systems, ensuring that integrations work consistently on Windows, Linux, and mainframes.
3. Optimized Performance for External Calls: Future REXX implementations could reduce the overhead of calling external programs by introducing efficient communication protocols, such as shared memory access or optimized inter-process communication (IPC).
4. Better Error Handling and Debugging Tools: Advanced debugging features, including error logging, real-time monitoring, and stack tracing for external calls, would make troubleshooting integration issues more efficient.
5. Enhanced Security Measures: Implementing built-in security mechanisms, such as sandboxed execution environments, restricted permissions for external calls, and validation for input/output operations, would reduce vulnerabilities.
6. Native Support for REST APIs and Web Services: Adding direct support for RESTful API calls and web service communication would allow REXX to interact seamlessly with modern cloud-based applications and data services.
7. Data Type and Structure Compatibility Improvements: Enhancing REXX to support advanced data formats (e.g., JSON, XML, Protocol Buffers) would simplify data exchange between REXX and other languages, reducing the need for complex conversion logic.
8. Integration with Modern Development Frameworks: Extending REXX to work with popular frameworks like .NET, Spring (Java), or Flask (Python) would make it easier to incorporate REXX into enterprise-level applications.
9. Support for Multithreading and Parallel Execution: Future enhancements could enable REXX to work with multithreaded applications, allowing better performance when interfacing with high-performance computing systems.
10. Automated Dependency Management: Introducing a package management system for REXX (similar to Python’s pip or Node.js’s npm) would simplify the installation and management of external libraries, making integration smoother.