===============
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>`_.

^^^^^^^^^^^^^^^^^^^^^^^^^^^
Download and compile D:YAML
^^^^^^^^^^^^^^^^^^^^^^^^^^^

The newest version of D:YAML can be found
`here <https://github.com/Kiith-Sa/D-YAML>`_. Download a source archive, extract
it, and move to the extracted directory.

D:YAML uses a modified version of the `CDC <http://dsource.org/projects/cdc/>`_ 
script for compilation. To compile D:YAML, you first need to build CDC.
Do this by typing the following command into the console::

   dmd cdc.d

Now compile D:YAML with CDC.
To do this on Unix/Linux, use the following command::

   ./cdc

On Windows::

   cdc.exe

This will compile the library to a file called ``libdyaml.a`` on Unix/Linux or
``libdyaml.lib`` on Windows.


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

Create a directory for your project and in that directory, create a file called
``input.yaml`` with the following contents:

.. 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 file called ``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 *yaml* 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 does not contain exactly 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 first, as it is a sequence, and use the 
*Node.as()* method on the second to read its value as an integer.

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

You can iterate over subnodes using *Node* as the iterated type, or specify 
the type subnodes are expected to have. D:YAML will automatically convert 
iterated subnodes 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.
D:YAML will try to return the scalar as this type, converting if needed, 
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 doesn't preserve style information in documents, so even though
``output.yaml`` will contain the same data as ``input.yaml``, it might be 
formatted differently. Comments are not preserved, either.


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

To compile your project, DMD needs to know which directories contain the
imported modules and the library. You also need to tell it to link with D:YAML.
The import directory should be the ``source`` subdirectory of the D:YAML
directory. You can specify it using the ``-I`` option of DMD. The library
directory should point to the compiled library. On Unix/Linux you can specify
it using the ``-L-L`` option, and link with D:YAML using the ``-L-l`` option.
On Windows, the import directory is used as the library directory. To link with
the library on Windows, just add the path to it relative to the current
directory.

For example, if you extracted and compiled D:YAML in ``/home/xxx/dyaml``, your
project is in ``/home/xxx/dyaml-project``, and you are currently in that 
directory, compile the project with the following command on Unix/Linux::

   dmd -I../dyaml/source -L-L../dyaml -L-ldyaml main.d

And the following on Windows::

   dmd -I../dyaml/source ../dyaml/libdyaml.lib main.d

This will produce an executable called ``main`` or ``main.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.
