==Summary==

YAVL-CPP is a C++ library check if a given YAML file follows an
expected schema. For example, you can use this to check if a
configuration file has the tree structure that your program
expects to have.

This library checks if the input YAML has the tree structure
(i.e., keys, values, types, nesting of keys) that the
specification expects. See example below.

To be clear, this is not a tool to check if the input file is a
valid YAML; any YAML parser will do that.

The tree specification file is also written in YAML.

This library saves you the hassle of writing code to emit error
messages about what is wrong about the input file. Your code
can be written assuming that it only ever works with input
that conforms to an expected schema.

Structures such as lists of lists, maps of lists,
lists etc can be nicely checked. :)

==Example Tree Specification==

{{{
map:
  HEADER:
    map:
      name: [string: ]
      version: [string: ]
      size: [enum: [big, small]]
      pieces:
        map:
          a:
            list: [string: ]
          b:
            list: [uint64: ]
}}}

Notice that HEADER.pieces.a is list nested within
the map HEADER.pieces. You can have arbitrary levels
of nesting, and also do things like maps within lists.

Note: one of the items in the [http://code.google.com/p/yavl-cpp/source/browse/trunk/TODO TODO] is to simplify this
syntax.

==Valid YAML==

{{{
HEADER:
  name: myname
  version: 1.02
  size: big
  pieces:
    a: [hello, world]
    b: [100, 200]
}}}

==Invalid YAML==

{{{
HEADER:
  name: myname
  version: 1.02
  size: xbig
  pieces:
    a: [hello, world]
    b: [x100, 200]
}}}

With the invalid YAML, you'll get an errors that 'xbig'
is not allowed and that 'x100' could not be converted to
a 'long long'.

==Dependencies==

Yavl-cpp uses the excellent [http://code.google.com/p/yaml-cpp/ yaml-cpp] library. Go check
out yaml-cpp just for the heck of it. It's one of the
best designed libraries out there (IMHO). Simple, and to the
point implementation and documentaion.

==Compilation==

Nothing fancy. Just compile in yavl.cpp and all the cpp files of
yaml-cpp with your program. I believe that libraries should pollute
your build process as little as possible (thankfully, so does
yaml-cpp).

Here is how you would compile the example checker program,
example-code/checker.cpp. YAML_CPP_DIR is where you
untarred the yaml-cpp source and YAVL_CPP_DIR is where
you untarred the yavl-cpp source.

{{{
g++ -I$YAML_CPP_DIR/include -I$YAVL_CPP_DIR/src \
  $YAML_CPP_DIR/src/*.cpp \
  $YAVL_CPP_DIR/src/yavl.cpp \
  $YAVL_CPP_DIR/example-code/checker.cpp -o checker
}}}

And run it like this:

{{{
checker $YAVL_CPP_DIR/example-specs/gr3.yaml $YAVL_CPP_DIR/example-specs/y0.gr3.yaml
}}}

==Developer Notes==

What I found interesting about this exercise was how short I was
able to make the checker program by a judicious selection of:

  * problem space restriction
  * treespec language is itself YAML
  
Problem space restriction gave the most bang. Instead of
solving a very general problem, I chose to solve a certain
subset of the problem. I think it's quite a large subset,
so hopefully many people will find this library useful.

By using YAML to encode the treespec, I saved myself the
hassle of writing a parser, and the user of the library
the hassle of learning yet another DSL.

eof