# MiniForth **Source:** https://github.com/ttsiodras/MiniForth GitHub - ttsiodras/MiniForth: A tiny Forth I built in a week. Blog post: https://www.thanassis.space/miniforth.html [Skip to content](#start-of-content) ## Navigation Menu Toggle navigation [Sign in](/login?return_to=https%3A%2F%2Fgithub.com%2Fttsiodras%2FMiniForth) Appearance settings * Platform + AI CODE CREATION - [GitHub CopilotWrite better code with AI](https://github.com/features/copilot) - [GitHub SparkBuild and deploy intelligent apps](https://github.com/features/spark) - [GitHub ModelsManage and compare prompts](https://github.com/features/models) - [MCP RegistryNewIntegrate external tools](https://github.com/mcp) + DEVELOPER WORKFLOWS - [ActionsAutomate any workflow](https://github.com/features/actions) - [CodespacesInstant dev environments](https://github.com/features/codespaces) - [IssuesPlan and track work](https://github.com/features/issues) - [Code ReviewManage code changes](https://github.com/features/code-review) + APPLICATION SECURITY - [GitHub Advanced SecurityFind and fix vulnerabilities](https://github.com/security/advanced-security) - [Code securitySecure your code as you build](https://github.com/security/advanced-security/code-security) - [Secret protectionStop leaks before they start](https://github.com/security/advanced-security/secret-protection) + EXPLORE - [Why GitHub](https://github.com/why-github) - [Documentation](https://docs.github.com) - [Blog](https://github.blog) - [Changelog](https://github.blog/changelog) - [Marketplace](https://github.com/marketplace) [View all features](https://github.com/features) * Solutions + BY COMPANY SIZE - [Enterprises](https://github.com/enterprise) - [Small and medium teams](https://github.com/team) - [Startups](https://github.com/enterprise/startups) - [Nonprofits](https://github.com/solutions/industry/nonprofits) + BY USE CASE - [App Modernization](https://github.com/solutions/use-case/app-modernization) - [DevSecOps](https://github.com/solutions/use-case/devsecops) - [DevOps](https://github.com/solutions/use-case/devops) - [CI/CD](https://github.com/solutions/use-case/ci-cd) - [View all use cases](https://github.com/solutions/use-case) + BY INDUSTRY - [Healthcare](https://github.com/solutions/industry/healthcare) - [Financial services](https://github.com/solutions/industry/financial-services) - [Manufacturing](https://github.com/solutions/industry/manufacturing) - [Government](https://github.com/solutions/industry/government) - [View all industries](https://github.com/solutions/industry) [View all solutions](https://github.com/solutions) * Resources + EXPLORE BY TOPIC - [AI](https://github.com/resources/articles?topic=ai) - [Software Development](https://github.com/resources/articles?topic=software-development) - [DevOps](https://github.com/resources/articles?topic=devops) - [Security](https://github.com/resources/articles?topic=security) - [View all topics](https://github.com/resources/articles) + EXPLORE BY TYPE - [Customer stories](https://github.com/customer-stories) - [Events & webinars](https://github.com/resources/events) - [Ebooks & reports](https://github.com/resources/whitepapers) - [Business insights](https://github.com/solutions/executive-insights) - [GitHub Skills](https://skills.github.com) + SUPPORT & SERVICES - [Documentation](https://docs.github.com) - [Customer support](https://support.github.com) - [Community forum](https://github.com/orgs/community/discussions) - [Trust center](https://github.com/trust-center) - [Partners](https://github.com/partners) * Open Source + COMMUNITY - [GitHub SponsorsFund open source developers](https://github.com/sponsors) + PROGRAMS - [Security Lab](https://securitylab.github.com) - [Maintainer Community](https://maintainers.github.com) - [Accelerator](https://github.com/accelerator) - [Archive Program](https://archiveprogram.github.com) + REPOSITORIES - [Topics](https://github.com/topics) - [Trending](https://github.com/trending) - [Collections](https://github.com/collections) * Enterprise + ENTERPRISE SOLUTIONS - [Enterprise platformAI-powered developer platform](https://github.com/enterprise) + AVAILABLE ADD-ONS - [GitHub Advanced SecurityEnterprise-grade security features](https://github.com/security/advanced-security) - [Copilot for BusinessEnterprise-grade AI features](https://github.com/features/copilot/copilot-business) - [Premium SupportEnterprise-grade 24/7 support](https://github.com/premium-support) * [Pricing](https://github.com/pricing) Search or jump to... # Search code, repositories, users, issues, pull requests... 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Blog post: ### License [MIT license](/ttsiodras/MiniForth/blob/master/LICENSE) [95 stars](/ttsiodras/MiniForth/stargazers) [7 forks](/ttsiodras/MiniForth/forks) [Branches](/ttsiodras/MiniForth/branches) [Tags](/ttsiodras/MiniForth/tags) [Activity](/ttsiodras/MiniForth/activity) [Star](/login?return_to=%2Fttsiodras%2FMiniForth) [Notifications](/login?return_to=%2Fttsiodras%2FMiniForth) You must be signed in to change notification settings * [Code](/ttsiodras/MiniForth) * [Issues 0](/ttsiodras/MiniForth/issues) * [Pull requests 0](/ttsiodras/MiniForth/pulls) * [Actions](/ttsiodras/MiniForth/actions) * [Projects 0](/ttsiodras/MiniForth/projects) * [Security 0](/ttsiodras/MiniForth/security) * [Insights](/ttsiodras/MiniForth/pulse) Additional navigation options * [Code](/ttsiodras/MiniForth) * [Issues](/ttsiodras/MiniForth/issues) * [Pull requests](/ttsiodras/MiniForth/pulls) * [Actions](/ttsiodras/MiniForth/actions) * [Projects](/ttsiodras/MiniForth/projects) * [Security](/ttsiodras/MiniForth/security) * [Insights](/ttsiodras/MiniForth/pulse) # ttsiodras/MiniForth master [Branches](/ttsiodras/MiniForth/branches)[Tags](/ttsiodras/MiniForth/tags) Go to file Code Open more actions menu ## Folders and files | Name | | Name | Last commit message | Last commit date | | --- | --- | --- | --- | --- | | Latest commit History[41 Commits](/ttsiodras/MiniForth/commits/master/) 41 Commits | | | | [contrib](/ttsiodras/MiniForth/tree/master/contrib "contrib") | | [contrib](/ttsiodras/MiniForth/tree/master/contrib "contrib") | | | | [simavr @ a56b550](/buserror/simavr/tree/a56b550872906a971ac128002772d90c9e30377d "simavr") | | [simavr @ a56b550](/buserror/simavr/tree/a56b550872906a971ac128002772d90c9e30377d "simavr") | | | | [src](/ttsiodras/MiniForth/tree/master/src "src") | | [src](/ttsiodras/MiniForth/tree/master/src "src") | | | | [src\_x86](/ttsiodras/MiniForth/tree/master/src_x86 "src_x86") | | [src\_x86](/ttsiodras/MiniForth/tree/master/src_x86 "src_x86") | | | | [testing](/ttsiodras/MiniForth/tree/master/testing "testing") | | [testing](/ttsiodras/MiniForth/tree/master/testing "testing") | | | | [.gitignore](/ttsiodras/MiniForth/blob/master/.gitignore ".gitignore") | | [.gitignore](/ttsiodras/MiniForth/blob/master/.gitignore ".gitignore") | | | | [.gitmodules](/ttsiodras/MiniForth/blob/master/.gitmodules ".gitmodules") | | [.gitmodules](/ttsiodras/MiniForth/blob/master/.gitmodules ".gitmodules") | | | | [LICENSE](/ttsiodras/MiniForth/blob/master/LICENSE "LICENSE") | | [LICENSE](/ttsiodras/MiniForth/blob/master/LICENSE "LICENSE") | | | | [Makefile](/ttsiodras/MiniForth/blob/master/Makefile "Makefile") | | [Makefile](/ttsiodras/MiniForth/blob/master/Makefile "Makefile") | | | | [README.md](/ttsiodras/MiniForth/blob/master/README.md "README.md") | | [README.md](/ttsiodras/MiniForth/blob/master/README.md "README.md") | | | | [config.mk](/ttsiodras/MiniForth/blob/master/config.mk "config.mk") | | [config.mk](/ttsiodras/MiniForth/blob/master/config.mk "config.mk") | | | | View all files | | | ## Repository files navigation * [README](#) * [MIT license](#) *( Wrote [a blog post about this here](https://www.thanassis.space/miniforth.html) )* It was raining hard, a week ago. And what could you possibly do on a rainy Saturday afternoon? Well... You can make a Forth interpreter/compiler from scratch... ...then put it inside a 1.5$ Blue Pill microcontroller... ...and finally, inside an Arduino UNO... ... within its tiny 2K RAM! Click on the image to watch it blinking the LED of my Arduino: [![Here's a video of it action, blinking my Arduino :-)](https://camo.githubusercontent.com/10dcc45a92a8eb1fbc79bbcf7127dea99324e316bf5b5ce1bd0515f9c86e5da5/68747470733a2f2f696d672e796f75747562652e636f6d2f76692f7865506f6c6c62437a6f772f302e6a7067)](https://www.youtube.com/watch?v=xePollbCzow) I haven't done anything even *remotely* close to this in decades... I *loved* building it. The rainy afternoon turned into a week-long hackfest *(was looking forward every day to the post-work FORTH-tinkering in the afternoon...)* The result: a tiny, mini, micro Forth. In portable C++ :-) It has... * basic arithmetic * star-slash (double-word accurate muldiv) * literals * constants * variables * direct memory access * string printing * reseting * comments * nested DO/LOOP * comparisons * nested IF/ELSE/THEN * ...and of course, functions (Forth words) Here's an ascii-cast recording of it in action: [![Recording of building and uploading on an Arduino UNO](https://camo.githubusercontent.com/429594b830bb91d714d4beb75bd9684a0108521b63c4a5669fa2ce955d2b396d/68747470733a2f2f61736369696e656d612e6f72672f612f3432333634392e737667)](https://asciinema.org/a/423649?autoplay=1) Read the test scenario below to see my supported Forth constructs. # Portability, ArduinoSTL and Valgrind/AddressSanitizer checks I meant it when I said "portable". Part of my reasoning was, that in addition to targeting multiple platforms (e.g. BluePill and Arduino) I wanted to be able to use Valgrind and AddressSanitizer to detect - in the host! - any issues I have with my memory handling. Since I had embedded targets in mind, I tried ArduinoSTL - but it was too wasteful memory-wise. It also made the build process significantly slower. I therefore built my own [memory pool, as well as list, tuple and string-like C++ templates](https://github.com/ttsiodras/MiniForth/tree/master/src/mini_stl.h). It was a nice challenge, re-inventing a tiny C++ STL... And I understand STL a lot better now, after building small pieces of it myself :-) # Simulation / Debugging I setup simulation via [simavr](https://github.com/buserror/simavr.git). This tremendously improved my developing speed, since a simulator spawns and runs much faster than the real board. Due to the code being portable, debugging took place mostly in the host GDB; and after Valgrind and AddressSanitizer gave their blessing, I usually found out that the simulator (and the real board) worked fine as well. # BluePill vs Arduino UNO Thanks to ArduinoSTL, I quickly reached the point of running inside the BluePill. The 1.5$ mini-monster has 10 times more SRAM than an Arduino UNO; so in a couple of days, I had a [working branch](https://github.com/ttsiodras/MiniForth/tree/BluePill-STM32F103C). [![The 1.5$ 'Beast'](/ttsiodras/MiniForth/raw/master/contrib/BluePill.jpg "The 1.5$ 'Beast'")](/ttsiodras/MiniForth/blob/master/contrib/BluePill.jpg) But as said above, that wasn't nearly enough to make it work in my Arduino UNO. That required far more work *(see below)*. As for the BluePill, I should note that, as in all my other embedded targets, I prefer a development workflow that is based on normal bootloaders *(not on programmers)*. I therefore burned the [stm32duino](https://github.com/rogerclarkmelbourne/STM32duino-bootloader) bootloader on the BluePill, which allowed me to easily program it in subsequent iterations via the USB connection (and a simple `make upload`). The same USB connection would then function as a serial port immediately afterwards - allowing me to interact with the newly uploaded Forth in the BluePill. The screenshot below is from a `tmux`: on the left, the output from `make upload`; and on the right, I used `picocom` to interact with my mini-Forth over the serial port: [![Compiling, uploading and testing](/ttsiodras/MiniForth/raw/master/contrib/itworks.jpg "Compiling, uploading and testing")](/ttsiodras/MiniForth/blob/master/contrib/itworks.jpg) # Memory - the final frontier That covered the first two days. But when I tried compiling for the Arduino UNO, I realised that the ArduinoSTL was not enough. I run out of memory... So I built my own [mini-STL](https://github.com/ttsiodras/MiniForth/tree/master/src/mini_stl.h), and tightly controlled *all* memory utilisation. I also used macro-magic to move all strings to Flash at compile-time (see `dprintf` in the code)... And saved memory everywhere I could, re-using error messages across various operations - and storing the entire array of native operations in Flash. Nothing flexes your coding muscles as much as optimising; whether it is for speed or for space. See the implementation of ".S" for example, where the (obvious) stack reversal code is also the most wasteful... Changing it to a slower but memory-preserving algorithm allowed me to use ".S" even when almost all my memory is full. # C++ vs C I know that many developers hate C++. I even wrote a [blog post](https://www.thanassis.space/cpp.html) about it. And I understand why - they see code like this... ``` #include "mini_stl.h" template typename forward_list::box *forward_list::_freeList = NULL; ``` ...and they start screaming - "what the hell is that", "incomprehensible madness", etc. But there are very important benefits in using C++ - and templates in particular. You write less code, with no additional run-time or memory overhead compared to C, and with a lot more compile-time checks that watch your back (for things that would otherwise blow up in your face). See my Optional for example, that emulates (badly) the optional type of Rust/OCaml/F#/Scala/Kotlin etc. It **forces** you to check your returned error codes: ``` Optional Forth::needs_a_number(const __FlashStringHelper *msg) { if (_stack.empty()) return error(emptyMsgFlash, msg); auto topVal = *_stack.begin(); if (topVal._kind == StackNode::LIT) return topVal._u.intVal; else return FAILURE; } ``` You can't "forget" to check the potential for a failure coded inside your returned value - because your code has to "unwrap" it. I could have done this better, but I chose to implement it via simple tuples (this was a one-weeks-afternoons hack, after all :-) As for the template "magic" incantation above - it *is* true magic: My `forward_list` template is using free-lists to store the `pop_front`-ed elements and reuse them in subsequent allocations. I wanted these free-lists to be global (i.e. static members) because lists of the same type must re-use a single, commonly-shared free-list. The magic spell tells the compiler I want to instantiate these globals *once*, for each type T that I use in any lists in my code. # My Forth test scenario - including a FizzBuzz! Yep, FizzBuzz - we are fully Turing complete. And would surely pass Joel's interview :-) ``` ." Reset... " RESET ." Check comments... " \ Yes, we support the new-style comments :-) ." Computing simple addition of 3 + 4... " 3 4 + . ." Is 1 = 2 ?... " 1 2 = . ." Is 1 > 2 ?... " 1 2 > . ." Is 1 < 2 ?... " 1 2 < . ." Define pi at double-word precision... " : pi 355 113 */ ; ." Use definition to compute 10K times PI... " 10000 pi . ." Check: 23 mod 7... " 23 7 MOD . ." Defining 1st level function1... " : x2 2 * ; ." Defining 1st level function2... " : p4 4 + ; ." 2nd level word using both - must print 24... " 10 x2 p4 . ." Defining a variable with value 123... " 123 variable ot3 ." Printing variable's value... " ot3 @ . ." Defining The Constant (TM)... " 42 constant lifeUniverse ." Printing The Constant (TM)... " lifeUniverse . ." Setting the variable to The Constant (TM)... " lifeUniverse ot3 ! ." Printing variable's value... " ot3 @ . ." Setting the variable to hex 0x11... " $11 ot3 ! ." Printing variable's value... " ot3 @ . ." Setting the variable to binary 10100101... " %10100101 ot3 ! ." Printing variable's value... " ot3 @ . ." Defining helper... " : p5 5 U.R . ; ." Defining 3 times loop... " : x3lp 3 0 DO I p5 LOOP ; ." Calling loop... " x3lp ." Defining loop calling loop 2 times... " : x6lp 2 0 DO x3lp LOOP ; ." Nested-looping 2x3 times... " x6lp ." Inline: " : m 3 1 DO 3 1 DO CR J p5 I p5 ." = " J I * p5 LOOP LOOP ; ." Use inline loops with two indexes... " m ." Make multiples of 7 via DUP... " : m7s 10 0 DO DUP I * . LOOP DROP ; ." Print them and DROP the 7... " 7 m7s ." Reset... " RESET \ Time for Turing completeness... ." Let's do Fizz-Buzz! " \ Turing Completeness check... \ fizz ( n -- 0_or_1 n ) ." Define fizz... " : fizz DUP 3 MOD 0 = IF ." fizz " 1 ELSE 0 THEN SWAP ; \ buzz ( n -- 0_or_1 n ) ." Define buzz... " : buzz DUP 5 MOD 0 = IF ." buzz " 1 ELSE 0 THEN SWAP ; \ emitNum ( 0_or_1 0_or_1 n -- ) ." Define emitNum... " : emitNum ROT ROT + 0 = if . ELSE DROP THEN ; \ mainloop ( n -- ) ." Define mainloop... " : mainloop ." ( " fizz buzz emitNum ." ) " ; \ fb ( -- ) ." Define fizzbuzz... " : fb 37 1 DO I mainloop LOOP ; ." Run it! " fb ." Report memory usage... " .S ." All done! " ``` # Automation I am a strong believer in automation. The final form of my `Makefile` therefore has many rules - e.g. `make arduino-sim` - that automate various parts of the workflow. Here's what they do: * **arduino**: Compiles the code for Arduino UNO - builds `src/tmp/myforth.ino.{elf,hex}` * **arduino-sim**: After building, launches the compiled mini-Forth in `simduino`. * **upload**: After building, uploads to an Arduino attached to the port configured inside `config.mk`. * **terminal**: After uploading, launches a `picocom` terminal with all appropriate settings to interact with my Forth. * **x86**: Builds for x86. Actually, should easily build for any native target (ARM, etc). * **test-address-sanitizer**: Uses the x86 binary to test the code, executing all steps of the scenario shown above. The binary is built with the address sanitizer enabled (to detect memory issues). * **test-valgrind**: Same, but with Valgrind. * **test-simulator**: Spawns `simavr` and sends the entire test scenario shown above to it - while showing the responses received from it. * **test-arduino**: Sends the entire test scenario shown above to an Arduino Uno connected to the port specified in `config.mk` and shows the responses received over that serial port. * **blink-arduino**: Sends the "hello word" of the HW world: a tiny [Forth program](/ttsiodras/MiniForth/blob/master/testing/blinky.fs) blinking the Arduino's LED. Another example of automation - the complete test scenario shown in the previous section, is not just an example in the documentation; it is extracted automatically from this README and fed into the Valgrind and AddressSanitizer tests... and also into the Python testing script that sends the data to the board in real-time. [DRY](https://en.wikipedia.org/wiki/Don%27t_repeat_yourself), folks. # Conclusion I thoroughly enjoyed building this. I know full well that Forths are not supposed to be built in C++; they are supposed to be built in assembly, and also, utilise the Flash to store the user-compiled code at run-time. But that wasn't the point of this - the point was to have fun and learn Forth. And what better way to learn a language than to actually implement it! :-) And... as a child of the 80s... I now know first-hand what [Jupiter Ace](https://en.wikipedia.org/wiki/Jupiter_Ace) was about :-) Fork the code, and enjoy tinkering with it! Thanassis. ## About A tiny Forth I built in a week. Blog post: ### Topics [arduino](/topics/arduino "Topic: arduino") [cpp](/topics/cpp "Topic: cpp") [forth](/topics/forth "Topic: forth") ### Resources [Readme](#readme-ov-file) ### License [MIT license](#MIT-1-ov-file) ### Uh oh! There was an error while loading. Please reload this page. 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