Skip to content

Latest commit

 

History

History

interpreter

README.md

< Back To Design Patterns

Interpreter Design Pattern

Please support my repo with your star.

Definition

The Interpreter Design Pattern is a behavioral pattern that defines a way to evaluate language grammar or expressions. It involves creating an interpreter for a simple language by defining a class for each grammar rule. These classes can interpret a given context or expression by recursively processing input based on the defined structure. It is particularly useful for parsing and executing instructions in languages or protocols.

Example in Real World/Nature Inspired

  1. Musical Notation Reading: Musicians interpret sheet music symbols to produce corresponding sounds, following a defined set of rules.
  2. Legal Documents: Lawyers and judges interpret the meaning of legal language based on rules and context.
  3. Body Language Interpretation: Humans "read" body language gestures (like a smile or crossed arms) and derive meaning based on cultural or contextual grammar.
  4. Recipes: A recipe book provides a set of structured instructions (ingredients, steps), and a cook interprets them to produce the dish.

Real Usage/System Design Problems

  1. Expression Evaluators (e.g., Calculators): Evaluating mathematical expressions like "2 + 3 * 5" by building an abstract syntax tree (AST) and interpreting it based on operator precedence.
  2. Query Languages: Systems like SQL parsers or search engines can use interpreter patterns to parse and execute simple command languages.
  3. DSLs (Domain Specific Languages): When creating small languages tailored for specific tasks (e.g., game scripting, build tools like Ant), interpreter patterns can help execute the domain-specific commands.

Important Points of Implementation

  • Define Grammar Rules with Classes: Each rule (terminal or non-terminal) is implemented as a class with an interpret method.
  • Use Composite Pattern: The pattern often uses Composite to build a tree representing the grammar and recursively interpret it.
  • Good for Simple Languages: Interpreter is ideal when the grammar is simple and unlikely to change often. For complex languages, other tools (like parser generators) are usually more efficient.
  • Can Become Hard to Maintain: As the language grows, maintaining many grammar classes can make the code hard to manage, suggesting a switch to more powerful parsing techniques.

< Back To Design Patterns