Interpreter Design Pattern

Bridging the Language Gap with Flexible Execution

In essence, the Interpreter Design Pattern opens a door to a world of custom languages and flexible execution within your software. It grants your users a unique voice and unlocks specialized functionalities, taking your application beyond the bounds of traditional programming.

Workflow

  1. Define a grammar for your Domain-Specific Languages (DSL). This specifies the valid structure and rules for constructing expressions within the language.
  2. Create abstract classes for different expression types. Each class represents a specific element in the grammar and defines an interprete() method.
  3. Concrete expression classes inherit from the abstract classes. These classes implement the interprete() method with the logic for evaluating each specific type of expression.
  4. Build a parser for your DSL. This component takes input written in the DSL and converts it into a tree structure of expression objects.
  5. The interpreter walks the expression tree. Starting from the root, it calls the interprete() method on each expression object, evaluating the entire instruction step-by-step.

Benefits

Example

from abc import ABC, abstractmethod

class Expression(ABC):
    @abstractmethod
    def interpret(self):
        pass

class Number(Expression):
    def __init__(self, value):
        self.value = value

    def interpret(self):
        return self.value

class Plus(Expression):
    def __init__(self, left, right):
        self.left = left
        self.right = right

    def interpret(self):
        return self.left.interpret() + self.right.interpret()

class Minus(Expression):
    def __init__(self, left, right):
        self.left = left
        self.right = right

    def interpret(self):
        return self.left.interpret() - self.right.interpret()

# Client code using the interpreter
expression = Plus(Number(3), Minus(Number(7), Number(2)))
result = expression.interpret()
print(result)  # Output: 8

Remember