🎶 Interpreter Pattern
Tags: swift, programming, computerscience, architecture
Published: 2022-12-13 17:18:58


![Interpreter Pattern](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/p0dg0rofdgx2ew5s1nfn.png)

---

The interpreter pattern is used to evaluate sentences in a language.

Github https://github.com/sergeyleschev/design-patterns

**Example**
```swift
protocol IntegerExpression {
    func evaluate(_ context: IntegerContext) -> Int
    func replace(character: Character, integerExpression: IntegerExpression) -> IntegerExpression
    func copied() -> IntegerExpression
}

final class IntegerContext {
    private var data: [Character:Int] = [:]

    func lookup(name: Character) -> Int {
        return self.data[name]!
    }

    func assign(expression: IntegerVariableExpression, value: Int) {
        self.data[expression.name] = value
    }
}

final class IntegerVariableExpression: IntegerExpression {
    let name: Character

    init(name: Character) {
        self.name = name
    }

    func evaluate(_ context: IntegerContext) -> Int {
        return context.lookup(name: self.name)
    }

    func replace(character name: Character, integerExpression: IntegerExpression) -> IntegerExpression {
        if name == self.name {
            return integerExpression.copied()
        } else {
            return IntegerVariableExpression(name: self.name)
        }
    }

    func copied() -> IntegerExpression {
        return IntegerVariableExpression(name: self.name)
    }
}

final class AddExpression: IntegerExpression {
    private var operand1: IntegerExpression
    private var operand2: IntegerExpression

    init(op1: IntegerExpression, op2: IntegerExpression) {
        self.operand1 = op1
        self.operand2 = op2
    }

    func evaluate(_ context: IntegerContext) -> Int {
        return self.operand1.evaluate(context) + self.operand2.evaluate(context)
    }

    func replace(character: Character, integerExpression: IntegerExpression) -> IntegerExpression {
        return AddExpression(op1: operand1.replace(character: character, integerExpression: integerExpression),
                             op2: operand2.replace(character: character, integerExpression: integerExpression))
    }

    func copied() -> IntegerExpression {
        return AddExpression(op1: self.operand1, op2: self.operand2)
    }
}
```
Usage
```swift
var context = IntegerContext()

var a = IntegerVariableExpression(name: "A")
var b = IntegerVariableExpression(name: "B")
var c = IntegerVariableExpression(name: "C")

var expression = AddExpression(op1: a, op2: AddExpression(op1: b, op2: c)) // a + (b + c)

context.assign(expression: a, value: 2)
context.assign(expression: b, value: 1)
context.assign(expression: c, value: 3)

var result = expression.evaluate(context)
```
Sources: [Github](https://github.com/sergeyleschev/design-patterns/tree/main/Interpreter)

> **_Behavioral_**
In software engineering, behavioral design patterns are design patterns that identify common communication patterns between objects and realize these patterns. By doing so, these patterns increase flexibility in carrying out this communication.
Source: [wikipedia.org](https://en.wikipedia.org/wiki/Behavioral_pattern)

---

🐝 [Chain Of Responsibility](https://dev.to/sergeyleschev/swift-design-patterns-chain-of-responsibility-4bbd)
👫 [Command Pattern](https://dev.to/sergeyleschev/swift-design-patterns-command-pattern-3044)
🎶 [Interpreter Pattern](https://dev.to/sergeyleschev/swift-design-patterns-interpreter-pattern-390a)
🍫 [Iterator Pattern](https://dev.to/sergeyleschev/swift-design-patterns-iterator-pattern-405o)
💐 [Mediator Pattern](https://dev.to/sergeyleschev/swift-design-patterns-mediator-pattern-4299)
💾 [Memento Pattern](https://dev.to/sergeyleschev/swift-design-patterns-memento-pattern-chp)
👓 [Observer Pattern](https://dev.to/sergeyleschev/swift-design-patterns-observer-pattern-44fc)
🐉 [State Pattern](https://dev.to/sergeyleschev/swift-design-patterns-state-pattern-5ej4)
💡 [Strategy Pattern](https://dev.to/sergeyleschev/swift-design-patterns-strategy-pattern-143c)
📝 [Template Method](https://dev.to/sergeyleschev/swift-design-patterns-template-method-1c2o)
🏃 [Visitor Pattern](https://dev.to/sergeyleschev/swift-design-patterns-visitor-pattern-4hl5)
🌰 [Abstract Factory](https://dev.to/sergeyleschev/swift-design-patterns-abstract-factory-3ppa)
👷 [Builder Pattern](https://dev.to/sergeyleschev/swift-design-patterns-builder-pattern-3609)
🏭 [Factory Method](https://dev.to/sergeyleschev/swift-design-patterns-factory-method-5c6e)
🔂 [Monostate Pattern](https://dev.to/sergeyleschev/swift-design-patterns-monostate-pattern-574i)
🃏 [Prototype Pattern](https://dev.to/sergeyleschev/swift-design-patterns-prototype-pattern-n25)
💍 [Singleton](https://dev.to/sergeyleschev/swift-design-patterns-singleton-3c8b)
🔌 [Adapter Pattern](https://dev.to/sergeyleschev/swift-design-patterns-adapter-pattern-1040)
🌉 [Bridge Pattern](https://dev.to/sergeyleschev/swift-design-patterns-bridge-pattern-1ee2)
🌿 [Composite Pattern](https://dev.to/sergeyleschev/swift-design-patterns-composite-pattern-1koj)
🍧 [Decorator Pattern](https://dev.to/sergeyleschev/swift-design-patterns-decorator-pattern-2c6p)
🎁 [Facade Pattern](https://dev.to/sergeyleschev/swift-design-patterns-facade-pattern-130a)
🍃 [Flyweight Pattern](https://dev.to/sergeyleschev/swift-design-patterns-flyweight-pattern-6ko)
☔ [Protection Proxy](https://dev.to/sergeyleschev/swift-design-patterns-protection-proxy-3kpc)
🍬 [Virtual Proxy](https://dev.to/sergeyleschev/swift-design-patterns-virtual-proxy-2bbg)

---

**Contacts**
I have a clear focus on time-to-market and don't prioritize technical debt. And I took part in the Pre-Sale/RFX activity as a System Architect, assessment efforts for Mobile (iOS-Swift, Android-Kotlin), Frontend (React-TypeScript) and Backend (NodeJS-.NET-PHP-Kafka-SQL-NoSQL). And I also formed the work of Pre-Sale as a CTO from Opportunity to Proposal via knowledge transfer to Successful Delivery.

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