1. Introduction
Is it possible to have a programming language that has no syntax? It sounds like a contradiction. Programming languages are all about syntax, plus a bit of code generation, optimization, run-time environment, and so on. But syntax is the most important part as far as programmers are concerned. When encountering a new programming language, it takes time to learn the syntax.
Could we just make the syntax disappear or at least make it as simple as possible? Could we also make the syntax arbitrary so that the programmer writing the code can define it for themselves?
Ouroboros is a programming language that tries to do just that. It has the simplest syntax ever. It is so simple that it does not even have a syntax analyzer. All it has is a lexical analyzer, which is 20 lines long.
At the same time, you can write complex programs and even expressions with parentheses and operators of different precedence, assuming you write your own syntax for that in the program. That way, no syntax also means any syntax.
This article is an introduction to Ouroboros, a programming language with no syntax. It is a toy, never meant to be used in production, but it is a fun toy to play with, especially if you have ever wanted to create your own programming language.
There were programming languages with minimal syntax. One of the very first languages was LISP, which used only parentheses to group statements as lists.
If you are familiar with TCL, you may remember how simple the language is. However, it still defines complex expressions and control structures as part of the language.
Another simple language to mention is FORTH. It is a stack language. The syntax is minimal. You either put something on the stack or call a function that works with the values on the stack. FORTH was also famous for its minimal assembly core and for the fact that the rest of the compiler was written in FORTH itself.
These languages inspired the design of Ouroboros. LISP is known for the simplest syntax. One might say that LISP has the simplest syntax of all programming languages, but it would be a mistake. True to its name, it uses parentheses to delimit lists, which can be either data or programming structures. As you may know, LISP stands for “Lots of Irritating Superfluous Parentheses.”
Ouroboros does not do that. It inherits the use of { and } from TCL, but unlike LISP, you are forced to use them only where they are really needed.
Ouroboros, although being an interpreted language, can compile itself. Well, not really compile, but you can define syntax for the language in the language itself. However, it is not like in the case of compilers where the compiler is written in the source language. One of the first compilers was the PASCAL compiler written by Niklaus Wirth in PASCAL. The C compiler was also written in C, and more and more language compilers are written in the language they compile.
In the case of an interpreted language, it is a bit different. It is not a separate program that reads the source code and generates machine code. It is the executing code, the application program itself, that becomes part of the interpreter.
That way, you cannot look at it and say: this code is not Ouroboros. Any code can be, depending on the syntax you define for it at the start of the code.
2. The Name of the Game
Before diving into what Ouroboros is, let’s talk about the name itself. Ouroboros coils around itself in an endless cycle of creation and recreation. The name “Ouroboros” is as multifaceted as the language itself, offering layers of meaning that reflect its unique nature and aspirations.
2.1. The Eternal Cycle
At its core, Ouroboros draws inspiration from the ancient symbol of a serpent consuming its own tail. This powerful image represents the cyclical nature of creation and destruction, perfectly encapsulating our language’s self-referential definition. Just as the serpent feeds upon itself to sustain its existence, Ouroboros the language is defined by its own constructs, creating a closed loop of logic and functionality.
2.2. UR: The Essence of Simplicity
Abbreviated as “UR,” Ouroboros embraces the concept of fundamental simplicity. In German, “Ur—” signifies something primordial, primitive, or in its most basic form. This perfectly encapsulates the design philosophy behind Ouroboros: a language stripped down to its absolute essentials.
By pushing the simplification of syntax to the extreme, Ouroboros aims to be the “ur-language” of programming—a return to the most elemental form of computation. Like the basic building blocks of life or the fundamental particles of physics, Ouroboros provides a minimal set of primitives from which complex structures can emerge.
This radical simplicity is not a limitation but a feature. It challenges programmers to think at the most fundamental level, fostering a deep understanding of computational processes. In Ouroboros, every construct is essential, every symbol significant. It’s programming distilled to its purest form.
2.3. Our Shared Creation
The name begins with “Our-,” emphasizing the collaborative nature of this language. Ouroboros is not just a tool but a shared endeavor that belongs to its community of developers and users. It’s a language crafted by us, for us, evolving through our collective efforts and insights.
2.4. Hidden Treasures
Delve deeper into the name, and you’ll uncover more linguistic gems:
“Oro” in many Romance languages means “gold” or “prayer.” Ouroboros can be seen as a golden thread of logic, or a prayer-like mantra of computational thought.
“Ob-” as a prefix often means “toward” or “about,” suggesting that Ouroboros is always oriented toward its own essence, constantly reflecting upon and refining itself.
“Boros” could be playfully interpreted as a variation of “bytes,” hinting at the language’s digital nature.
Parsing the name as “our-ob-oros” reveals a delightful multilingual wordplay: “our way to the treasure.” This blend of English (“our”), Latin (“ob” meaning “towards”), and Greek (“oros,” which can be associated with “boundaries” or “definitions”) mirrors the language’s eclectic inspirations.
Just as Ouroboros draws from the diverse traditions of TCL, LISP, and FORTH, its name weaves together linguistic elements from different cultures. This multilingual, multi-paradigm approach guides us toward the treasures of computation, defining new boundaries along the way, much like how TCL offers flexibility, LISP promotes expressiveness, and FORTH emphasizes simplicity and extensibility.
2.5. A Name That Bites Back
Ultimately, Ouroboros is a name that challenges you to think recursively, to see the end in the beginning and the whole in every part. It’s a linguistic puzzle that mirrors the very nature of the programming language it represents—complex, self-referential, and endlessly fascinating.
As you embark on your journey with Ouroboros, remember that you’re not just writing code; you’re participating in an ancient cycle of creation, where every end is a new beginning, and every line of code feeds into the greater whole of computational possibility.
3. What is Ouroboros
Ouroboros is a programming language that has no syntax. I have already said that, and now comes the moment of truth: it is a “lie.” There is no programming language with absolutely no syntax. UR has a syntax, and it is defined with this sentence:
You write the lexical elements of the language one after the other.
3.1. Syntax
That is all.
When the interpreter starts to execute the code, it begins reading the lexical elements one after the other. It reads as many elements as it needs to execute some code and not more. To be specific, it reads exactly one lexical element before starting execution. When the execution triggered by the element is finished, it goes on reading the next element.
The execution itself can trigger more reads if the command needs more elements. We will see it in the next example soon.
A lexical element can be a number, a string, a symbol, or a word. Symbols and words can and should have an associated command to execute.
For example, the command puts is borrowed shamelessly from TCL and is associated with the command that prints out a string.
puts “Hello, World!”
It is the simplest program in Ouroboros. When the command behind puts starts to execute, it asks the interpreter to read the next element and evaluate it. In this example, it is a constant string, so it is not difficult to calculate. The value of a constant string is the string itself.
The next example is a bit more complex:
puts add “Hello, ” “World!”
In this case, the argument to the command puts is another command: add. When puts asks the interpreter to get its argument, the interpreter reads the next element and then starts to execute. As add starts to execute, it needs two arguments, which it asks from the interpreter. Since these arguments are strings, add concatenates them and returns the result.
3.2. Blocks
There is a special command denoted by the symbol {. The lexical analyzer recognizing this character will ask the interpreter to read the following elements until it finds the closing }. This call is recursive in nature if there are embedded blocks.
The resulting command is a block command. A block command executes all the commands in it and results in the last result of the commands in the block.
puts add {“Hello, ” “World!”}
If we close the two strings into a block, then the output will be a single World! without the `Hello, `. The block “executes” both strings, but the value of the block is only the second string.
3.3. Commands
The commands implemented are documented in the readme of the project on GitHub. The actual set of commands is not fascinating. Every language has a set of commands.
The fascinating part is that in UR there is no difference between functions and commands. Are puts or add commands or functions? How about if and while? They are all commands, and they are not part of the language per se. They are part of the implementation.
The command if asks the interpreter to fetch one argument, evaluated. It will use this as the condition. After this, it will fetch the next two elements without evaluation. Based on the boolean interpretation of the condition, it will ask the interpreter to evaluate one of the two arguments.
Similarly, the command while will fetch two arguments without evaluation. It then evaluates the first as a condition, and if it is true, it will evaluate the second and then go back to the condition. It fetched the condition unevaluated because it will need to evaluate it again and again. In the case of the if command, the condition is evaluated only once, so we did not need a reference to the unevaluated version.
Many commands use the unevaluated version of the arguments. This use makes it possible to use the “binary” operators as multi-argument operators. If you want to add up three numbers, you can write add add 1 2 3, or add* 1 2 3 {}, or {add* 1 2 3}. The command add fetches the first argument unevaluated and sees if it is a *. If it is *, then it will fetch the arguments until it encounters the end of the arguments or an empty block.
This is a little syntactic sugar, which should be peculiar in the case of a language that has no syntax. It really is there to make the experiment and the playing with the language bearable. On the other side, it erodes the purity of the language. It is also only a technical detail, and I mention it only because we will need to understand it when we discuss the metamorphic nature of the language. It will be needed to understand the use of the first example there.
3.4. Variables
UR supports variables. Variables are strings with values associated with them. The value can be any object.
When the interpreter sees a symbol or a bare word (identifier) to evaluate, it will check the value associated with it. If the value is a command, then it will execute the command. In other cases, it will return the value.
The variables are scoped. If you set a variable in a block, then the variable is visible only in that block. If there are variables with the same name in the parent block, then the variable in the child block will shadow the variable in the parent block.
Variable handling and scoping are implementation details and not strictly part of the language.
The implementation as it is now supports boolean, long, double, big integer, big decimal, and string primitive values. It also supports lists and objects.
A list is a list of values, and it can be created with the list command. The argument to the command is a block. The command list will ask the interpreter to fetch the argument unevaluated. Afterward, it evaluates the block from the start the same way as the block command does. However, instead of throwing away the resulting values and returning the last one, it returns a list of the results.
An object is a map of values. It can be created with the object command. The argument to the command is the parent object. The fields of the parent object are copied to the new object.
Objects also have methods. They are the fields that have a command as a value.
4. Introspection
The interpreter is open like a cracked safe after a heist. Nothing is hard-wired into the language. When I wrote that the language interpreter recognizes bare words, symbols, strings, etc., it was only true for the initial setup. The lexical analyzers implemented are UR commands, and they can be redefined. They are associated with the names $keyword, $string, $number, $space, $block, $blockClose, and $symbol. The interpreter uses the variable structures to find these commands. There is another variable named $lex that is a list of the lexical analyzers.
The interpreter uses this list when it needs to read the next lexical element. It invokes the first, then the second, and so on until one of them returns a non-null value, a lexical element, which is a command.
If you modify this list, then you can change the lexical analyzers, and that way you can change the syntax of the language.
The simplest example is changing the interpretation of the end-of-line character.
You may remember that we can use the binary operators using multiple arguments terminated with an empty block. It would be nice if we could omit the block and just write add* 1 2 3 simply adding a new-line at the end. We can do that by changing the lexical analyzer that recognizes the end-of-line character, and this is exactly what we are going to do in this example.
set q add* 3 2
1 {} puts q
insert $lex 0 ‘{
if { eq at source 0 “\n”}
{sets substring 1 length source source ‘{}}}
set q add* 3 2
1 {} puts q
We insert a new lexical analyzer at the beginning of the list. If the very first character of the current state of the source code is a new-line character, then the lexical analyzer eats this character and returns an empty block.
The command source returns the source code that was not parsed by the interpreter yet. The command sets sets the source code to the string value specified.
The first puts q will print 6 because at the time of the first calculation, new-lines are just ignored, and that way the value of q is add* 3 2 1 {}. The second puts q will print 5 because the new-line is eaten by the lexical analyzer, and the value of q is add* 3 2 {}. Here, the closing {} was the result of the lexical analysis of the new-line character. The values 1 and {} on the next line are calculated, but they do not have any effect.
This is a very simple example. If you want to see something more complex, the project file src/test/resources/samples/xpression.ur contains a script that defines a numerical expression parser.
There is a special command called fixup. This command forces the interpreter to parse the rest of the source. After this point, the lexical analyzers are not used anymore.
Executing this command does not give any performance benefit, and that is not the purpose. It is more like a declaration that all the codes that are part of the source code introspection and the metamorphic calculation are done. A special implementation of the command can also take the parsed code and generate an executable, turning the interpreter into a compiler.
5. Technical Considerations
The current version is implemented in Java. Ouroboros is not a JVM language, though. We do not compile the code to Java byte-code. The Java code interprets the source and executes it.
The implementation is an MVP focusing on the metamorphic nature of the language. It is meant to be an experiment. This is the reason why there are no file, network, and other I/O operations except the single puts command that writes to the standard output.
The Java service loader feature is used to load the commands and to register them with their respective names in the interpreter. It means that implementing extra commands is as simple as creating them, writing a class implementing a ContextAgent to register them (see the source code), and putting them on the classpath.
The whole code is open-source and available on GitHub. It is licensed under the Apache License 2.0 (see the license file in the repo). It is exactly 100 classes at the time of writing this article. It means that the source code is simple, short, and easy to understand. If you need some straightforward scripting language in your application, you can use it. It was not meant to be for production, though.
6. Going Further
There is no plan currently to extend the language and include more commands. We only plan to create more metamorphic code in the language. The reason for that is that we do not see the language as a practical tool as of today. If it proves to be useful and gains a user base and utilization, we certainly will incorporate more commands to support I/O, file handling, networking, and so on.
We also have visions of implementing the interpreter in other languages, like in Rust and Go. Anyone suggesting or wanting to develop commands for better usability or adding features is welcome. It can be a parallel project, or it can be merged into the main project if that makes sense.
7. Conclusion
In exploring Ouroboros, we delved into the concept of a programming language that minimizes syntax to the point of almost non-existence. This radical approach challenges the conventional understanding of what a programming language should be, presenting a system where syntax is both absent and infinitely customizable. By drawing inspiration from languages like LISP, TCL, and FORTH, Ouroboros embodies simplicity and introspection, allowing programmers to define their syntax and commands within the language itself.
While Ouroboros is not designed for practical production use, it serves as an intriguing experiment in language design and metaprogramming. Its self-referential nature and minimalistic design offer a playground for developers interested in the fundamentals of computation, syntax design, and language interpretation. Whether it evolves into a more robust tool or remains a fascinating intellectual exercise, Ouroboros pushes the boundaries of how we think about programming languages, inviting us to consider the possibility of a language where syntax is as mutable and recursive as the Ouroboros serpent itself.
Programming Language with no Syntax?
