ARCHITECTURE.md

Architecture

The implementation is based on a modified version of Edsger Dijkstra's Shunting Yard algorithm that produces an expression tree instead of a postfix notation.

For example this expression:

expression = "not @a or @b and not @c or not @d or @e and @f"

Would parse into this expression tree:

# Get the root of the tree - an Expression object.
expressionNode = parser.parse(expression)

            or
          /    \
        or      and
       /  \    /   \
     or  not  @e    @f
    /  \    \
  not  and   @d
 /    /   \
@a   @b   not
             \
              @c

The root node of tree can then be evaluated for different combinations of tags. For example:

result = expressionNode.evaluate(["@a", "@c", "@d"]) # => false