Interpreter

The interpreter pattern is specific implimentation of the composite pattern generally used for language parsing. In the interpreter pattern a class is produced for each symbol in the language. A statement can then be broken down into a syntax tree of these classes which can in turn be used to interpret the statement.

Use When

You should use Interpreter when there is a language that you need to interpret and when the statements of the language can be represented as abstract syntax trees. It works best when:

• the grammar of the language is simple. Otherwise, the class hierarchy for the grammar becomes large and complex.
• efficiency is not essential.

Structure

(from wikipedia)

Related Patterns

• Composite: The abstract syntax tree uses a Composite pattern.
• Flyweight: This pattern can be used to share the terminal symbols.
• Iterator: This pattern can be used to traverse the Interpreter structure.
• Visitor: This pattern can be used to collect the behavior for all abstract syntax tree nodes in one class.