YAML DOM

IMPORTANT!!! This project has been shit-canned because Crystal can't polymorph enumeration over Array and Hash. That makes this kind of API, while already difficult (because Crystal is a strongly typed language), essentially impossible. Sorry kids, you are stuck with pull parsing.

Intermediate Representation

The YAML DOM library provides a YAML composer that the models YAML Intermediate Representation. This model preserves information lost when using the current Crystal "parser". In particular tag information is preserved and accessible.

Installation

Add this to your application's shard.yml:

dependencies:
  yamldom:
    github: trans/yamldom.cr

Usage

First, lets see how we can get the intermediate representation of a YAML document.

require "yamldom"

yaml = <<-YAML
--- !foo
- EXAMPLE
- 100
YAML

doc = YAML.compose(yaml)
doc.tag    #=> "!foo"
doc.value  #=> ["EXAMPLE", "100"]
doc.class  #=> YAML::Sequence

There are a few things to notice here. First we were able to get the tag. Second, the class of object compose retuirns a YAML::Node and there are three types of such nodes, YAML::Scalar, YAML::Sequence and YAML::Mapping. If we look at the elements inside the sequence we will see it is made up of other nodes.

doc.value.node(0).to_s   #=> "EXAMPLE"
doc.value.node(0).class  #=> YAML::Scalar

We use #node to access the node itself. For convenience the usual #[] method accesses the underlying value.

doc.value[0]        #=> "EXAMPLE"
doc.value[0].class  #=> String

This makes it fairly easy to work with the DOM API.

Lastly note that the value 100 in the document is still a String.

doc.value[0]        #=> "100"

It isn't an Integer because composition is a stage before construction in which the node would be converted to a native data type (and extra information like tag lost).