EO compilation process consists of several steps covered in details in this blog post. Most of the steps have various files (.eo, .xmir, etc.) as their input/output, and sometimes it’s very handy to have them persisted somewhere for reuse between compilation runs. ~/.eo/ folder acts as such persistent storage. Let’s have a closer look at its structure and how it is bound to compilation process.

EO library provides an ability to generate pseudo-random sequences. It’s analogous to Random class in Java or random module in Python.
Let’s explore how this facility (exposed via org.eolang.math.random object) can be used in EO.

Since 0.25.0 version it is possible to use error object just like this:

[x] > check
  if. > @
    x.eq 0
    error "Can't divide by zero"
    42.div x

Here, the object error causes program termination at the first attempt to dataize it. It encapsulates any other object, which can play the role of an exception that is floating to the upper level.

The object try enables the catching of an error objects and extracting exceptions from them. For example, the following code prints “The 1th argument of ‘int.div’ is invalid: division by zero is infinity” and then “finally”:

QQ.try
  []
    42.div 0 > @
  [e]
    QQ.io.stdout > @
      e
  []
    QQ.io.stdout > @
      "finally"

The object error encapsulates the error message from int.div object and terminates the program.

The entire process of packaging EO objects and atoms into JAR artifacts is explained in this blog post: Objectionary: Dictionary and Factory for EO Objects. It’s pretty straight forward. However, there is one tricky situation related to placing compiled Java binaries into the JAR. This process may go wrong and sometimes it does. In version 0.24.0 of our Maven plugin we introduced a pair of options for the unplace goal. Here is how they work.

Since 0.23.16 version it is possible to use switch object just like this:

memory "swordfish" > password

QQ.switch
  *
    password.eq "swordfish"
    "password is correct!"
  *
    password.eq ""
    "empty password is not allowed"
  *
    FALSE
    "password is wrong"

Here, switch object returns “password is correct!”, which is the first true case in this statement. The switch object consists of arrays with arrays of two elements: condition and return value.

If the above parameters are missing, switch will return an error object with msg as a string message.

When you compile your EO code, the compiler discovers which objects are “foreign” and tries to find them in Objectionary. It finds them, downloads, and then compiles locally. The problem is that the objects in Objectionary are not static: they get new versions very often. That’s why, in order to stabilize your build you may want to use their fixed versions.

Since 0.23.15 version it is possible to use number object just like this:

# this is 7
(QQ.math.number -7).abs 

It is a decorator of int and float objects with the following additional attributes:

There is eoc, a command line tool that helps you automate compilation, transpilation, and execution of simple EO programms. With this tool you can also create and execute unit tests. Just name them *-test.eo and add metas +junit to them.