Hello World

You have just downloaded Open Dylan and installed it in /opt/opendylan. So how do you write the canonical Hello World app? This example assumes the bash shell is used. You may need to adjust for your local shell.

$ export PATH=/opt/opendylan/bin:$PATH
$ make-dylan-app hello-world
$ cd hello-world
$ dylan-compiler -build hello-world.lid
...lots of output...
$ _build/bin/hello-world
Hello, world!

Ta da! Now a quick review of the steps with a little bit of explanation.

First you must set PATH so that make-dylan-app and dylan-compiler will be found. ./_build/bin is where dylan-compiler puts the executables it builds.

Note

Some of these differ on Windows, so please be sure to read Notes for Windows Users if you are on Windows.

make-dylan-app creates a directory with the same name as the project, and four files:

  1. hello-world.lid – This says what other files are part of the project. The order in which the files are listed here determines the order in which the code in them is executed.

  2. library.dylan contains the library and module definitions. These can be extended as your project grows more complex.

  3. hello-world.dylan contains the main program. Note that the last top-level definition is a call to the main function, which may have any name; there is no predefined “main” function that is automatically called.

  4. registry/<platform>/hello-world is a “registry file”, which contains the path to the hello-world.lid file.

The first time you build hello-world it builds all used libraries, all the way down to the dylan library itself. Subsequent compiles only need to recompile hello-world itself and are therefore much faster.

dylan-compiler has a batch mode and an interactive mode. The -build option says to build the project in batch mode. When you pass a “.lid” file to the compiler it builds the library described by that file. In the next section you’ll see that you can also pass the name of the project (without “.lid”) and it will use “registries” to find the project sources.

The compiler places its output in the _build directory in the current working directory. This includes the libraries and executables that it builds. You can run the executable as noted above from this location.