dyaml/docsrc/tutorials/getting_started.rst

===============
Getting started
===============

Welcome to D:YAML! D:YAML is a `YAML <http://en.wikipedia.org/wiki/YAML>`_ parser
library for the `D programming language <http://dlang.org>`_.  This tutorial will
explain how to set D:YAML up and use it in your projects.

This is meant to be the **simplest possible** introduction to D:YAML. Some of this
information might already be known to you. Only basic usage is covered.


----------
Setting up
----------

^^^^^^^^^^^^^^^^^^^^^^^^
Install the DMD compiler
^^^^^^^^^^^^^^^^^^^^^^^^

Digital Mars D compiler, or DMD, is the most commonly used D compiler. You can find its
newest version `here <http://dlang.org/download.html>`_.  Download the version of DMD
for your operating system and install it.

.. note::
   Other D compilers exist, such as
   `GDC <http://gdcproject.org/>`_ and
   `LDC <http://bitbucket.org/goshawk/gdc/wiki/Home>`_.

^^^^^^^^^^^
Install dub
^^^^^^^^^^^

`dub <http://code.dlang.org/about>`_ is a build system and package manager for D.
It is the standard way to manage D projects and their dependencies, compilation and so
on.

DMD may include DUB in future releases, but at this point we need to install it
separately. See
`installation instructions <https://github.com/D-Programming-Language/dub#installation>`_.


-------------------------
Your first D:YAML project
-------------------------

Create a directory for your project and in that directory, create a new file named
``input.yaml`` and paste this code into the file:

.. code-block:: yaml

   Hello World : [Hello, World]
   Answer: 42

This will serve as input for our example.

Now we need to parse it. Create a new file with name ``main.d``. Paste following code
into the file:

.. code-block:: d

   import std.stdio;
   import yaml;

   void main()
   {
       //Read the input.
       Node root = Loader("input.yaml").load();

       //Display the data read.
       foreach(string word; root["Hello World"])
       {
           writeln(word);
       }
       writeln("The answer is ", root["Answer"].as!int);

       //Dump the loaded document to output.yaml.
       Dumper("output.yaml").dump(root);
   }


^^^^^^^^^^^^^^^^^^^^^^^
Explanation of the code
^^^^^^^^^^^^^^^^^^^^^^^

First, we import the *dyaml.all* module. This is the only D:YAML module you need to
import - it automatically imports all needed modules.

Next we load the file using the *Loader.load()* method. *Loader* is a struct used for
parsing YAML documents. The *load()* method loads the file as **one** YAML document, or
throws *YAMLException*, D:YAML exception type, if the file could not be parsed or
contains more than one document.  Note that we don't do any error checking here in order
to keep the example as simple as possible.

*Node* represents a node in a YAML document. It can be a sequence (array), mapping
(associative array) or a scalar (value). Here the root node is a mapping, and we use the
index operator to get subnodes with keys "Hello World" and "Answer". We iterate over the
former, as it is a sequence, and use the *Node.as()* method on the latter to read its
value as an integer.

You can iterate over a mapping or sequence as if it was an associative or normal array,
respectively.  If you try to iterate over a scalar, it will throw a *YAMLException*.

You can iterate using *Node* as the iterated type, or specify the type iterated nodes
are expected to have. D:YAML will automatically convert to that type if possible. Here
we specify the *string* type, so we iterate over the "Hello World" sequence as an array
of strings. If it is not possible to convert to iterated type, a *YAMLException* is
thrown. For instance, if we specified *int* here, we would get an error, as "Hello"
cannot be converted to an integer.

The *Node.as()* method is used to read value of a scalar node as specified type.  If the
scalar does not have the specified type, D:YAML will try to convert it, throwing
*YAMLException* if not possible.

Finally we dump the document we just read to ``output.yaml`` with the *Dumper.dump()*
method. *Dumper* is a struct used to dump YAML documents.  The *dump()* method writes
one or more documents to a file, throwing *YAMLException* if the file could not be
written to.

D:YAML tries to preserve style information in documents so e.g.  ``[Hello, World]`` is
not turned into:

| ``- Hello``
| ``- World``

However, comments are not preserved and neither are any extra formatting whitespace that
doesn't affect the meaning of YAML contents.


^^^^^^^^^
Compiling
^^^^^^^^^

We're going to use dub, which we installed at the beginning, to compile our project.

Create a file called ``dub.json`` with the following contents:

.. code-block:: json 

   {
       "name": "getting-started",
       "targetType": "executable",
       "sourceFiles": ["main.d"],
       "mainSourceFile": "main.d",
       "dependencies":
       {
           "dyaml": { "version" : "~>0.5.0", "path" : "../../"},
       },
   }

This file tells dub that we're building an executable called ``getting-started`` from
a D source file ``main.d``, and that our project depends on D:YAML 0.5.0 or any newer,
bugfix release of D:YAML 0.5 . DUB will automatically find and download the correct
version of D:YAML when the project is built.

Now run the following command in your project's directory::

   dub build

dub will automatically download D:YAML and compile it, and then then it will compile our
program.  This will generate an executable called ``getting-started`` or
``getting-started.exe`` in your directory.  When you run it, it should produce the
following output::

   Hello
   World
   The answer is 42


^^^^^^^^^^
Conclusion
^^^^^^^^^^

You should now have a basic idea about how to use D:YAML. To learn more, look at the
`API documentation <../api/index.html>`_ and other tutorials. You can find code for this
example in the ``example/getting_started`` directory in the package.