gforth

Opening the app — the first screen

You install the app, tap the icon, and three icons appear in your app drawer. One is labeled "Gforth fast," another "Gforth ITC," and the third is a net2o demo with an octopus icon. This is not a single app. It is a suite. The fast engine is for everyday use. The ITC engine is for debugging, with a single-step debugger and precise backtraces. The net2o demo is a protocol demonstration — a work in progress. You tap the fast engine, and a terminal opens. A spinning wheel appears. The app is unpacking the Gforth sources to your storage. This takes a few seconds, maybe longer. The spinner spins, but the app cannot respond to input while it works. When it finishes, you see a prompt. You are inside a Forth interpreter.

The app is called gforth - GNU Forth for Android. It is developed by Bernd Paysan, based in Munich, Germany. The app is free, open-source, and licensed under GPLv3. It is a binary distribution of the GNU Forth programming language for Android. It supports ARM and x86 processors. The app requires Android 4.1 or higher. It is small — around 6 MB. The app is not a game. It is not a tool for casual users. It is a programming environment for Forth, a stack-based language that has been around since the 1970s.

The app's terminal uses OpenGL. It renders colored ASCII characters using a fragment shader. This is unusual for a programming environment. Most terminals use software rendering. Gforth uses the GPU. This makes the terminal fast. The terminal also supports touch input. The menu button toggles the software keyboard. You can change the font size using a command: 3e gl-fscale makes the font three times larger. The app also runs a telnet server on port 4444. You can connect to it from another device and program remotely.

How the three engines work together

The three launcher icons serve different purposes. The fast engine is the default. It is optimized for speed. It uses a direct threaded interpreter with GCC optimizations. This is the engine you use for most tasks. The ITC engine stands for Indirect Threaded Code. It is slower, but it includes a debugger. You can step through your code, inspect the stack, and trace backtraces precisely, even on exceptions. This is useful when your program crashes. The net2o demo is a protocol demonstration. net2o is a networking protocol developed by Bernd Paysan. The demo is a proof of concept. It shows how Gforth can be used for networked applications. The developer warns that it is a demo, so do not expect it to work flawlessly.

The app's file system is structured around the /sdcard/gforth/ directory. When you first run the app, it unpacks the Gforth source code and examples to this location. The examples are stored in /sdcard/gforth/<version>/minos2/. This includes OpenGL demos, video playback examples, and a slideshow viewer. The app also creates a /sdcard/gforth/home/ directory for your personal files. You can place your own Forth programs here and load them with the include command. The app's file paths are configurable. You can use .fpath to see where Gforth searches for files.

The original analysis — the three icons and the Android file system

The app's three icons are a clever design. They separate concerns. The fast engine is for performance. The debug engine is for development. The net2o demo is for experimentation. This separation is useful, but it also creates confusion. New users may not know which icon to tap. The app's description does not explain the difference clearly. Users who tap the net2o demo may be disappointed when it does not work perfectly. Users who tap the ITC engine may wonder why it is slower. The app could benefit from better onboarding.

The app's reliance on the /sdcard/ directory is a problem on newer Android versions. Google has restricted access to external storage. Apps can no longer write to /sdcard/ without permission. The app requests storage permissions, but users may not grant them. If the app cannot write to /sdcard/, it cannot unpack the source code. This is why the app crashes on some devices. The developer is aware of this issue. The changelog for version 0.7.9_20251001 says: "Removed permission request for photos and videos as Google demanded." This is a partial fix. The app still needs storage access to function properly.

The app's file system is also a source of complaints. Users report that the gforth folder is not found on storage after installation. The app unpacks the files, but users cannot find them. This is because the files are stored in a location that is not accessible to standard file managers. The app uses a private directory. Users need to use a file manager with root access or connect to a computer to access the files. This is a significant limitation for users who want to edit their Forth programs on the device.

Real-world performance and the limitations

The app performs well on supported devices. The fast engine is genuinely fast. The OpenGL terminal is smooth and responsive. The app does not contain ads. It does not collect data. It is a clean, focused programming environment. However, the app has limitations. The most significant is the permission issue. The app requests unusual permissions: location, camera, microphone, and storage. These permissions are not clearly explained. Users are right to be suspicious. The app does not need location or camera access to run Forth. These permissions are likely remnants of the net2o demo or the OpenGL implementation. The developer should remove them or explain them clearly.

The app also has compatibility issues. It crashes on Android 12 and later. This is due to Google's changes to the file system and permissions. The developer is working on fixes, but the app is not fully compatible with the latest Android versions. Users on Android 11 or earlier report that the app works well. Users on Android 12 or later may experience crashes or failures to start. The app's version history shows that the developer is actively maintaining it. The latest update was in November 2025. This is a positive sign.

The app's editor is basic. It does not have syntax highlighting. It does not support paste via long press. You cannot change the font size from the settings menu. You have to use a command. This is not user-friendly. The app is designed for programmers who are comfortable with the command line. It is not for beginners. The app is a tool for experts. It is a powerful tool, but it requires a learning curve. The app is a faithful implementation of Gforth on Android. It does what it promises. It just does not do it in a way that is accessible to everyone.