Created: 2008-02-22 08:41
Updated: 2019-02-28 19:59
License: other

The Io Language

Note: This document is intended to be used as a reference for setting up and configuring Io. For a guide on how to use the language itself, please visit the website at

Table of Contents

What is Io?

Io is a dynamic prototype-based programming language in the same realm as Smalltalk and Self. It revolves around the idea of message passing from object to object.

For further information, the programming guide and reference manual can be found in the docs folder.

Quick Links


From a Package Manager

Io is currently only packaged for OS X. To install it, open a terminal and type:

brew install io

Note that this package may not be as updated as the version from the source repository.

From Source

Linux Build Instructions

First, make sure that this repo and all of its submodules have been cloned to your computer by running git clone with the --recursive flag:

git clone --recursive

Io uses the CMake build system and supports all of the normal flags and features provided by CMake. To prepare the project for building, run the following commands:

cd io/           # To get into the cloned folder
mkdir build      # To contain the CMake data
cd build/
cmake ..         # This populates the build folder with a Makefile and all of the related things necessary to begin building

In a production environment, pass the flag -DCMAKE_BUILD_TYPE=release to the cmake command to ensure that the C compiler does the proper optimizations. Without this flag, Io is built in debug mode without standard C optimizations.

To install to a different folder than /usr/local/bin/, pass the flag -DCMAKE_INSTALL_PREFIX=/path/to/your/folder/ to the cmake command.

To build without Eerie, the Io package manager, pass the flag -DWITHOUT_EERIE=1 to the cmake command.

Once CMake has finished preparing the build environment, ensure you are inside the build folder, and run:

sudo make install

This should build and install the Io language and Eerie, the Io package manager. Io can then be run with the io command and Eerie can be run with the eerie command.

Note About Building Eerie

Running eerie after installing with sudo make install may shoot back an error such as this one:

Exception: unable to open file path '/home/<user>/.eerie/config.json': Permission denied
openForUpdating            77
Object Eerie                         eerie 3
CLI doFile                  140
CLI run                              IoState_runCLI() 1

If this occurs, this is because the ~/.eerie/ folder isn't accessible due to your user permissions. To fix this, go to your home folder and run:

sudo chown -R <your username>:<your username> .eerie/

OS X Build Instructions

See the Linux build instructions.

Windows Build Instructions

For all the different methods explained here, some of the addons won't compile as they depend on libraries not provided by Io.

For methods A and B you must download and install CMake (at least v2.8) from here:

For method C you must install the CMake Cygwin package (at least v2.8) using the Cygwin package installer.

For the make install command, if you are on Windows 7/Vista you will need to run your command prompts as Administrator: right-click on the command prompt launcher->"Run as administrator" or something similar)

You will also need to add <install_drive>:\<install_directory>\bin and <install_drive>:\<install_directory>\lib to your PATH environment variable.

Building with MSVC

  1. Install Microsoft Visual C++ 2008 Express (should work with other versions).

  2. Install Microsoft Windows SDK 7.0 (or newer).

  3. Install CMake (v2.8 at least)

  4. Run "Visual Studio 2008 Command Prompt" from the "Microsoft Visual Studio 2008" start menu.

  5. cd to <install_drive>:\Microsoft SDKs\Windows\v7.0\Setup then run: WindowsSdkVer.exe -version:v7.0

  6. Close the command prompt window and run step 4 again

  7. Ensure CMake bin path is in the PATH environment variable (eg: echo %PATH% and see that the folder is there) if not you will have to add it to your PATH.

  8. cd to your Io root folder

  9. We want to do an out-of-source build, so: mkdir buildroot and cd buildroot

  10. a) cmake ..


    b) cmake -DCMAKE_INSTALL_PREFIX=<install_drive>:\<install_directory> .. (eg: cmake -DCMAKE_INSTALL_PREFIX=C:\Io ..)

  11. nmake

  12. nmake install

Building with MinGW

For automatic MinGW install:

For non-automatic MinGW install and detailed instructions refer to:

  1. cd to your Io root folder

  2. We want to do an out-of-source build, so: mkdir buildroot and cd buildroot

  3. a) cmake -G"MSYS Makefiles" ..


    b) cmake -G"MSYS Makefiles" -DCMAKE_INSTALL_PREFIX=<install_drive>:/<install_directory> .. (eg: cmake -G"MSYS Makefiles" -DCMAKE_INSTALL_PREFIX=C:/Io ..)

  4. make

  5. make install

Building with MinGW-W64

  1. cd to your Io root folder

  2. We want to do an out-of-source build, so: mkdir buildroot and cd buildroot

  3. a) cmake -G"MinGW Makefiles" ..


    b) cmake -G"MinGW Makefiles" -DCMAKE_INSTALL_PREFIX=<install_drive>:/<install_directory> .. (eg: cmake -G"MinGW Makefiles" -DCMAKE_INSTALL_PREFIX=C:/Io ..)

  4. mingw32-make install

Building with Cygwin

Install Cygwin from:

  1. cd to your Io root folder

  2. We want to do an out-of-source build, so: mkdir buildroot and cd buildroot

  3. a) cmake ..


    b) cmake -DCMAKE_INSTALL_PREFIX=<install_drive>:/<install_directory> .. (eg: cmake -DCMAKE_INSTALL_PREFIX=C:/Io ..)

  4. make

  5. make install

Note: If you also have CMake 2.8 for Windows installed (apart from CMake for Cygwin) check your PATH environment variable so you won't be running CMake for Windows instead of Cygwin version.

Running Tests

You should be inside your out-of-source build dir. The vm tests can be run with the command:

io ../libs/iovm/tests/correctness/

Installing Addons

Many of the common features provided by the Io language aren't prepackaged in the Io core. Instead, these features are contained in addons that get loaded when launching the Io VM. In the past, these addons were automatically installed by the build process, but now they must be installed through Eerie, the Io package manager.

Most of these addons are housed under the IoLanguage group on GitHub:

To install an addon, ensure both Io and Eerie are installed correctly, then run:

eerie install <link to the git repository>

For example, to build and install the Range addon, run the command:

eerie install

To ensure that an addon installed correctly, pull up an Io interpreter and type the name of the object provided by the addon. It should load dynamically and automatically into the interpreter session, populating a slot in Lobby Protos Addons. Here is an example recording of how to install an addon into Io.

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