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Jupiter Programming Language

Jupiter is A dynamic object-oriented programming language based on Smalltalk/Self.


  • A set of simple core types:
    • Decimal floating point Numbers to avoid this:
    • Strings.
    • Arrays: Number indexed collections.
    • Maps: String indexed collections.
  • Immutable data structures.
  • There are no classes. Objects are created copying other objects ( prototypes ). Thanks to immutability no special semantics is needed to achieve this.
  • Unix friendly: Its source code is stored in files, which is not the 'Smalltalk way', but this allow us easy interaction with other Unix tools, like git, grep, IDE's/text editors etc.. See Juno IDE.
  • Generational garbage collector: The immutable data structures generate a lot a short-lived objects, using a generational GC improves the performance of collecting and reusing these temporal objects.
  • Tail call optimization: Recursive methods are the only way to make loops in Jupiter. This optimization make tail recursive calls as efficient as a imperative loops.
  • Compile inline if expressions. If expressions can be implemented as a regular message/method call in Smalltalk, but this is not very efficient, so Jupiter transform if expression into jump bytecodes.

Juno IDE

For a better programming experience (or at least more similar to other Smalltalk environments), you can use the Juno IDE

Some examples

"The traditional hello world program"
'Hello world!' print
"double a list of numbers"
numbers := {1,2,3}.
double := numbers map: [ :number | number * 2 ].
double == {2,4,6}
"sum two point objects"
aPoint := 1 @ 2. otherPoint := 2 @ 2. sum := aPoint + otherPoint

Check the tests ( in lib/core/src/core/tests/ ) for more examples

Differences with other Smalltalk systems


The Jupiter syntax is mostly the same as other smalltalk implementations, with a few differences:

  • No need to declare local variables
  • Local variables cannot be reassigned ( a := a + 1 won't work )
  • No Static Array syntax
  • Elements in dynamic Arrays are separated by comas
  • No return symbol. Methods return the last evaluated expression.


The object model is similar to Self. Jupiter has no classes, all objects are created copying other objects.

An Object in Jupiter is just an immutable persistent key-value collection of objects. The messages sent to objects don't modify the state of the object, instead return a new object with the updated state, therefore creating instances of objects ( cloning or copying prototypes ) is trivial.

Build requirements

Setting the JUPITERHOME environment variable

The interpreter needs this environment variable to load the core library. (In the future this won't be necesary, when proper installation scrips and/or packages are provided )

Navigate to the project folder:

$ cd jupiter-master/
$ export JUPITERHOME=$PWD/lib

Docs and Tutorial

Coming soon...


This project is yet in alpha state, so it may crash/leak memory/explode from time to time.


This project is licensed under the MPL-2.0 License. See the LICENSE file for details


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