De (Dynamic Expression) module provides means to build and evaluate dynamic expression of arbitrary complecity and operands/operators nature.

Expression is considered as tree consisted of operands and operators. Operater must have child nodes. Operand is terminal node.

Tree example:

(a + b) * c + d

- +
--- *
----- +
------- a
------- b
--- d

Here "+" and "*" are operators,
"a", "b" and "d" are operands

Expression tree structure is built with the help of <rubytree> gem (rubygems.org/gems/rubytree)

In addition to basic classes of Expression, Operand and Operator module provides some extensions for different nature expressions:

- Boolean expressions
- Sunspot Solr search expressions