Interpreter Pattern

Interpreter Design Pattern

Intent

    Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
    Map a domain to a language, the language to a grammar, and the grammar to a hierarchical object-oriented design.

Rules of thumb
    Considered in its most general form (i.e. an operation distributed over a class hierarchy based on the Composite pattern), nearly every use of the Composite pattern will also contain the Interpreter pattern. But the Interpreter pattern should be reserved for those cases in which you want to think of this class hierarchy as defining a language.
    Interpreter can use State to define parsing contexts.
    The abstract syntax tree of Interpreter is a Composite (therefore Iterator and Visitor are also applicable).
    Terminal symbols within Interpreter’s abstract syntax tree can be shared with Flyweight.
    The pattern doesn’t address parsing. When the grammar is very complex, other techniques (such as a parser) are more appropriate.


http://sourcemaking.com/design_patterns/interpreter


Interpreter pattern
the interpreter pattern is a design pattern that specifies how to evaluate sentences in a language. The basic idea is to have a class for each symbol (terminal or nonterminal) in a specialized computer language. The syntax tree of a sentence in the language is an instance of the composite pattern and is used to evaluate (interpret) the sentence
http://en.wikipedia.org/wiki/Interpreter_pattern